GENETIC METHOD FOR CONTROLLING SPROUTING

Abstract: This invention relates to a method of controlling sprout formation in plants and parts thereof including vegetative storage organs. The method involves the use of target and organ specific promoters to control expression of DNA sequences to inhibit sprouting. Sprouting is restored by switching on expression of DNA sequences using inducible promoter regions where sprouting may be controlled by, for example, application of an external chemical stimulus.

Description: GENETIC METHOD FOR CONTROLLING SPROUTING The present invention relates to a method of controlling sprout formation in plants and parts thereof including vegetative storage organs. Potato tubers are of major economic importance. They represent a carbohydrate resource for many diets and are used as a basis for a variety of processed products. Besides starch, tubers contain high-quality proteins, substantial amounts of vitamins, minerals and trace elements. Continuous production of potato tubers throughout the year is impossible in most regions where potatoes are grown. As a consequence storage of the harvested tubers is required. One of the potentially most damaging phenomena during storage is premature sprouting. Long term storage involves cooling, forced ventilation and use of chemical sprouting suppressants. The problems directly linked to long term storage are manifold. Cooling, usually done in Northern Europe by ventilation with air at ambient temperature is one of the methods to inhibit sprouting. Apart from the associated costs, longer term cooling at 4°C gives rise to the problems of cold sweetening and melanisation (darkening). Chemical sprouting suppressants are currently the only possibility for inhibiting sprouting in potatoes destined for processing and fresh consumption, since low temperature storage leads to unacceptable accumulation of reducing sugars. However, in recent years, questions have arisen as to the environmental and nutritional impact of chemical suppressants such as chlorinated hydrocarbons. There is therefore a real need for an alternative method of controlling sprouting in vegetative storage organs such as tubers. An alternative approach to delay sprouting would be the use of transgenic plants with a prolonged quiescence period. Sprouting of potato tubers involves several independent steps which might be targets for genetic engineering. The first step is the mobilisation of reserves, mainly starch. Starch breakdown occurs in amyloplasts and is mediated by starch phosphorylase and/or amylases. In the next step following starch breakdown, the resultant hexoses and/or hexose-phosphates have to be exported from amyloplasts. After transfer into the cytosol the produced hexoses and hexose-phosphates are distributed between glycolysis and sucrose synthesis. The third step is the formation of sucrose in the cytosol. Sucrose synthesis is energy dependent thus glycolysis and respiration are required. The fourth step is the transport of sucrose to the developing sprout. Finally the imported sucrose is utilised in the sprout to support growth and development. We have now developed a means of controlling sprouting in vegetative storage organs such that sprouting may be turned off and on without any undesirable side effects such as yield loss. This new method involves the targeted expression of genes resulting in the disruption of sprouting in combination with gene switch technology to restore sprouting when required. According to a first aspect of the present invention there is provided a method for the selective induction or suppression of sprouting in a plant comprising incorporating, preferably stably incorporating, into the genome of said plant by transformation a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region whereby the DNA sequence(s) in said first polynucleotide sequence is expressed during dormancy of the vegetative organ derived from said transgenic plant resulting in effective suppression of sprouting and the said suppression is neutralised by inducing expression of the DNA sequence(s) in said second polynucleotide sequence from said controllable promoter region by external application of an inducing substance such that restoration of sprouting of said vegetative storage organ is dependent on the application of the inducer. As used herein the term "tissue or organ selective promoter region" denotes those promoter regions which yield preferential expression of the DNA sequence(s) of interest in the desired tissue or organs. The DNA sequences in the DNA construct may be endogenous or heterologous with respect to the transformed host. Examples of DNA sequences which may be used in the method of the present invention to control sprouting include those DNA sequences coding for proteins involved in the mobilisation of reserves during dormancy such as the breakdown of storage compounds e.g starch breakdown, i.e starch phosphorylase, amylase (e.g.α or β amylase) and maltase; e.g in glycolysis and subsequent metabolism e.g phosphofructokinase, hexokinase; in sucrose biosynthesis e.g sucrose synthase; in the transport of reserves during dormancy such as in phloem loading e.g ATPase; in long distance phloem transport and in phloem unloading e.g inorganic pyrophosphorylase (iPPase); and in the utilisation of reserves during dormancy such as in assimilate breakdown e.g the breakdown of sucrose in the growing sprout, i.e invertase; and in the utilisation of assimilates e.g utilisation of sucrose-derived metabolites, in the provision of energy required for sprout formation e.g. DNA sequences coding for proteins involved in mitochondrial function such as in respiration, such as mitochondrial enzymes and transport proteins such as translocators e.g. adenine nucleotide translocator (ANT) and malate oxoglutarate translocator (MOT) and inhibitors thereof such as uncoupling proteins. Examples of useful DNA sequences also include any other sequences which are involved in potato sprouting Examples of preferred DNA sequences which may be used in the method of the present invention to control sprouting include those resulting in the production of sense, anti- sense or partial sense sequence(s) to, and/or coding for, proteins involved in the mobilisation and/or utilisation of sucrose, in potato sprouting and in mitochondrial function, such as in respiration. Examples of particularly preferred DNA sequences include those coding for an invertase derived from plant, bacterial or fungal sources e.g. from yeast, a pyrophosphatase derived from plant, bacterial or fungal sources and proteins involved in mitochondrial function such as MOT and ANT derived from plant, bacterial or fungal sources which are described hereinafter. Suppression of sprouting may be achieved in a variety of ways. The first DNA sequence(s) may be expressed during dormancy of the vegetative storage organ and then down-regulated when sprouting is desired. When sprouting is desired expression of the second DNA sequence(s) is turned on leading to down regulation of the first DNA sequence and consequently restoration of sprouting. Down regulation of a desired DNA sequence(s) may be achieved using methods well known in the art such as, for example, by use of repressor proteins, sense, anti-sense, partial - sense, and expression of a complementary protein. Examples of suitable operator/repressor systems include for example the lac, tet or lambda 434 systems and mutants thereof such as the Lac IΔ His mutant (Lehming, N., Sartoris, J., Niemoeller, M., Genenger, G., v. Wilcken- Bergman, B. and Muller-Hill, Benno (1987), EMBO J. 6(10) 3145-3153 - where the mutant has a change in amino acid 17 of Lac I altering tyrosine for histidine). Alternatively, an Amplicon™ may be used to down-regulate genes (Angell, S.M., Baulcombe, D.C, (1997) U 3675-3684). In this regard, the cDNA of replicating potato virus (PVX) RNA which has a transgene inserted therein is used whereby transiently expressed RNA sharing homology with the transgene is suppressed. Alternatively, expression of the DNA sequence(s) in the first polynucleotide sequence may result in the production of a sense, anti-sense or partial-sense sequence(s) which acts to suppress a gene involved in sprouting or in the expression of an Amplicon™. In this case sprouting is restored by switching on expression of the DNA sequence(s) in the second polynucleotide sequence which results in production of the protein or a corresponding protein to that, the production of which was suppressed by the sense, anti-sense or partial- sense sequence(s) in the first DNA sequence. Sprouting may also be restored by means of a suitable operator/repressor system. Where either or both of the polynucleotide sequences in the construct comprise more than one DNA sequence it is preferable that they are not identical to avoid any co- suppression effects. Expression of the DNA sequence(s) in the first polynucleotide sequence is under the control of a tissue or organ selective promoter to ensure targeted expression of the DNA sequence whereby expression is induced in an organ or tissue specific manner. Examples of tissue selective promoters include phloem selective promoters e.g. the rolC promoter, and examples of organ selective promoters include tuber specific promoters, such as the patatin promoter. The use of tissue or organ selective promoters such as the rolC and tuber promoters is particularly preferred. The DNA sequence(s) in the second polynucleotide sequence of the construct is under the control of a controllable promoter region. As used herein the term "controllable promoter region" includes promoters which may be induced chemically. The use of a promoter sequence which is controlled by the application of an external chemical stimulus is most especially preferred. The external chemical stimulus is preferably an agriculturally acceptable chemical, the use of which is compatible with agricultural practice and is not detrimental to plants or mammals. The controllable promoter region most preferably comprises an inducible switch promoter system as such as, for example, a two component system such as the alcAJ ' alcR gene switch promoter system described in our published International Patent Application No. WO 93/21334; the GST promoter as described in our published International Patent Application Nos. WO 90/08826 and WO 93/031294; and the ecdysone switch system as described in our published International Patent Application No. WO 96/37609, the teachings of which are incorporated herein by reference. Such promoter systems are herein referred to "switch promoters". The switch chemicals used in conjunction with the switch promoters are agriculturally acceptable chemicals making this system particularly useful in the method of the present invention. In the case of the alcA/alcR promoter switch system the preferred chemical inducer is ethanol in either liquid or more preferably in the vapour form. One of the main advantages of the use of ethanol vapour is that only small quantities of ethanol are required and that high levels of expression are achieved. Full details of switch chemicals are provided in the patent applications listed immediately above. Suitable transcription terminators which may be used are also well known in the art and include for example the nopaline synthase terminator and octopine synthase terminators. The promoter is most desirably a late tuber specific promoter which is active late in the dormancy period i.e just before sprouting. The controllable promoter region for use in the method of the present invention is preferably the GST or alcJi/ alcR promoter switch system. Restoration of sprouting is preferably achieved using switchable antisense or switchable sense or partial sense methods as is described more fully herein or alternatively by use of an Amplicon™ or by means of a suitable operator/repressor system. Down-regulation of gene activity due to partial sense co- suppression is described in our International Patent Application No. WO 91/08299 the teachings of which are incorporated herein and this may be avoided if necessary by using gene sequences derived from different organisms. According to a second aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide sequence comprises a DNA sequence coding for a protein involved in mobilisation and/or utilisation of sucrose and said second polynucleotide sequence comprises a DNA sequence which is a sense, an anti-sense or partial sense sequence corresponding to said protein or a DNA sequence which is capable of causing suppression of said protein. According to a third aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide sequence comprises a first DNA sequence coding for a protein involved in mobilisation and/or utilisation of sucrose and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and the second polynucleotide sequence comprises a DNA sequence coding for a repressor protein capable of binding to said operator sequence. According to a fourth aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in potato sprouting or a DNA sequence which is capable of causing suppression of a protein involved in potato sprouting and said second polynucleotide sequence comprises a DNA sequence(s) coding for a protein involved in potato sprouting. According to a fifth aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a first DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in potato sprouting or a DNA sequence which is capable of causing suppression of a protein involved in potato sprouting and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and said second polynucleotide sequence comprises a DNA sequence(s) coding for a repressor protein capable of binding to said operator sequence. According to a sixth aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in mitochondrial function or a DNA sequence which is capable of causing suppression of a protein involved in mitochondrial function and said second polynucleotide sequence comprises a DNA sequence(s) coding for a protein involved in mitochondrial function. According to a seventh aspect of the present invention there is provided a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a first DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in mitochondrial function or a DNA sequence which is capable of causing suppression of a protein involved in mitochondrial function and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and said second polynucleotide sequence comprises a DNA sequence(s) coding for a repressor protein capable of binding to said operator sequence. We have found the following combination of DNA sequences to be particularly suitable for use in the method of the invention: by placing a DNA sequence coding for an invertase under the control of a phloem selective promoter such as the rolC promoter, it is possible to target expression of the DNA sequence to the phloem and effectively repress sprouting and to then restore sprouting by switching on a DNA sequence coding for invertase anti-sense using the alc alcR chemical switch promoter. Sucrose concentration in the phloem from the leaf is so high that the effects of invertase expression are effectively swamped avoiding any unwanted side effects. This contrasts with the situation in the sprout phloem where expression of invertase has a dominant effect with the result that sucrose is broken down and sprouting is effectively inhibited. A further useful combination is a DNA sequence coding for an inorganic pyrophosphatase (iPPase) under the control of a tuber promoter. Uptake of sucrose and transport in the phloem is an energy requiring process and by inhibiting the provision of energy by expressing the DNA sequence coding for inorganic pyrophosphatase it is possible to inhibit the uptake process. The inhibition can be reversed by using, for example, an alcA alcR chemically induced switch promoter to switch on a DNA sequence coding for an antisense, sense or partial sense sequence to iPPase and sprouting is restored. Again the use of a tissue or organ selective promoter ensures that the inhibition of sucrose uptake and transport in the phloem does not occur in the whole plant but only in the tuber thereby minimising any deleterious effects in the plant. In both cases, an alternative means of restoring sprouting is by the use of an Amplicon™ where transiently expressed RNA sharing homology with the transgene is suppressed. Such a transgene could, for example, be a cDNA for an invertase or iPPase. A further alternative means of restoring sprouting is by the use of a suitable operator/repressor system. We have also found that by selectively inhibiting the provision of energy required for sprout growth and development in the tuber by placing a DNA sequence coding for sense, antisense or partial sense to a DNA sequence coding for a protein involved in mitochondrial function, such as the adenosine nucleotide translocator protein (ANT) or mitochondrial oxoglutarate translocator (MOT), under the control of a tuber selective promoter sprouting may be inhibited without unwanted side effects. Alternatively, a DNA sequence which causes suppression of such proteins may be used. One way in which reversal of the inhibition may be achieved is by switching on expression of a second DNA sequence the product of which is complementary to the first DNA sequence, for example a DNA sequence coding for ANT derived from a different source preferably from Arabidopsis may be used to counteract the effect of the ANT antisense expression. In the case of MOT a suitable complementary sequence may be derived from Panicum miliaceum as is described by Taniguchi and Sugiyama in Plant Molec.Biol. 30, 51-64 (1996). Alternatively, a suitable operator/ repressor system may be used to reverse inhibition. As above the alcA/ alcR chemical switch promoter may be used. The above examples are described more fully herein. According to some embodiments of the present invention the first polynucleotide sequence comprises a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and the second polynucleotide sequence comprises a DNA sequence coding for a repressor capable of binding to the operator sequence under the control of a switch promoter such that application of the inducer results in expression of the DNA sequence coding for the repressor which subsequently binds to the operator and expression of the first DNA sequence in the first polynucleotide sequence is switched off. An example of such a system is the lactose operator and repressor protein as is described in published International patent Application No. WO 90/08830. Other examples include the tetracycline and lambda 434 operator/repressor systems. Plant cells may be transformed with recombinant DNA constructs according to a variety of known methods for example, Agrobacterium Ti plasmids, electroporation, microinjection and by microprojectile gun. The transformed cells may then, in suitable cases, be regenerated into whole plants in which the new nuclear material is incorporated, preferably stably incorporated, into the genome. Both transformed monocotyledonous and dicotyledenous plants may be obtained in this way. According to an eighth aspect of the present invention, there is provided a plant cell transformed with any one of the DNA constructs defined above. According to a nineth aspect of the present invention there is also provided a whole plant transformed with a DNA construct according to the above aspects of the present invention wherein said DNA construct is incorporated, preferably stably incorporated, into the genome of said plant. The invention still further includes, according to a tenth aspect of the present invention, progeny of the plants of the preceding paragraph which progeny comprise a DNA construct according to the above aspects of the present invention incorporated, preferably stably incorporated, into their genome and the seeds and tubers of such plants and such progeny. The method of the present invention is particularly suitable for controlling sprouting in potato tubers. In a preferred embodiment the invention provides a method for the selective induction or suppression of sprouting in potatoes comprising stably incorporating into the genome of said potato by transformation a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region whereby the DNA sequence(s) in said first polynucleotide sequence is expressed during dormancy of the tuber derived from said transgenic potato resulting in effective suppression of sprouting and the said suppression is neutralised by inducing expression of the DNA sequence(s) in said second polynucleotide sequence from said controllable promoter region by external application of an inducing substance such that restoration of sprouting of said tuber is dependent on the application of the inducer. We have also identified five particularly preferred DNA sequences which we believe may also be especially useful in the method of the present invention. We have identified these DNA sequences as being induced during tuber storage and we have designated these as 16-3 (sequence 2), 16-8 (sequence 3), 10-1 (sequence 4) and AC4 (sequence 5), M-l-1 (MOT) (sequence in Figure 19) and a MOT variant (sequence 6 - having an EMBL Accession number X99853). The DNA sequences and their isolation are described fully in the accompanying examples. The present invention therefore provides, according to a further aspect, the use of all or part of the DNA sequences from clones 16-3, 10-1, AC4, 16- 8, M-l-1 and the MOT variant in a method according to the invention to control sprouting in plants. The DNA sequences of 16-3, 16-8, AC4 and M-l-1 are believed to be new and a twelfth aspect of the present invention extends to polynucleotides comprising nucleotides 1 to 870 in sequence 2 (corresponding to 16-3), nucleotides 1 to 712 in sequence 3 (corresponding to 16-8) or nucleotides 1 to 386 in sequence 5 (corresponding to AC4) or nucleotides 1 to 1351 in sequence Figure 19 (corresponding to M-l-1 encoding a MOT) and further to the protein products encoded thereby and to those proteins having a substantially similar activity and having an amino acid sequence which is at least 85% similar to the said product. It is preferred that the degree of similarity is at least 90%. and it is more preferred that the degree of similarity is 95% and it is most preferred that the degree of similarity is 97%. A particularly preferred embodiment of the polynucleotides consists of nucleotides 55 to 751 in sequence 2, nucleotides 87 to 473 in sequence 3, and to nucleotides 192 to 1164 in Figure 19 and further to the translation products encoded thereby and to those proteins having a substantially similar activity and having an amino acid sequence which is at least 85% similar to the said product. It is preferred that the degree of similarity is at least 90%. and it is more preferred that the degree of similarity is 95% and it is most preferred that the degree of similarity is 97%. As used herein the term "degree of similarity" is used to denote sequences which when aligned have similar (identical or conservatively replaced) amino acids in like positions or regions, where identical or conservatively replaced amino acids are those which do not alter the activity or function of the protein as compared to the starting protein. For example, two amino acid sequences with at least 85% similarity to each other have at least 85% similar (identical or conservatively replaced amino residues) in a like position when aligned optimally allowing for up to 3 gaps, with the proviso that in respect of the gaps a total of not more than 15 amino acid resides is affected. The degree of similarity may be determined using methods well known in the art (see, for example, Wilbur, W.J. and Lipman, D.J. "Rapid Similarity Searches of Nucleic Acid and Protein Data Banks." Proceedings of the National Academy of Sciences USA 80, 726-730 (1983) and Myers E.and Miller W. "Optimal Alignments in Linear Space". Comput. Appl. Biosci. 4:11-17(1988)). One programme which may be used in determining the degree of similarity is the MegAlign Lipman-Pearson one pair method (using default parameters) which can be obtained from DNAstar Inc, 1228, Selfpark Street, Madison, Wisconsin, 53715, USA as part of the Lasergene system. According to a thirteenth aspect of the present invention there is provided polynucleotide sequence(s) encoding a protein having a substantially similar activity to that encoded by nucleotides provided in sequences 2, 3 and 5 and Figure 19, which polynucleotide is complementary to one which still hybridises with the sequence comprised by that provided in sequences 2,3 or 5 or Figure 19 when incubated at or between low and high stringency conditions. In general terms, low stringency conditions can be defined as 3 x SSC at about ambient temperature to about 65 C and high stringency conditions as 0.1 x SSC at about 65°C. SSC refers to the buffer 0.15M Na CI, 0.015M trisodium citrate and 3 x SSC is three times as strong as SSC and 0.1 x SSC is one tenth of the strength of SSC. The invention further provides polynucleotide sequence(s) encoding a protein having a substantially similar activity to that encoded by nucleotides 55 to 751 in sequence 2, nucleotides 87 to 473 in sequence 3, or to nucleotides 192 to 1164 in Figure 19, which polynucleotide is complementary to one which still hybridises with the sequence comprised by nucleotides 55 to 751 in sequence 2, nucleotides 87 to 473 in sequence 3, or to nucleotides 192 to 1164 in Figure 19 when incubated at or between low and high stringency conditions. In general terms, low stringency conditions can be defined as 3 x SSC at about ambient temperature to about 65 C and high stringency conditions as 0.1 x SSC at about 65°C. SSC refers to the buffer 0.15M Na CI, 0.015M trisodium citrate and 3 x SSC is three times as strong as SSC and 0.1 x SSC is one tenth of the strength of SSC. The polynucleotides according to the present invention depicted in sequences 2, 3 and 5 and Figure 19 may be operably linked to a promoter region which may be homologous or heterologous to the polynucleotide and the present invention extends to such constructs. The present invention also extends to a DNA construct comprising said polynucleotides further comprising a region encoding a peptide which is capable of targeting the translation products of the polynucleotide to desired cellular or sub-cellular locations. The invention further provides a vector comprising said polynucleotide sequence as described in sequences 2, 3, 5 and Figure 19 preferably operably linked to a promoter region and optionally to a transcription terminator and or a targeting sequence as described above. The sequences provided herein for 16-3, 16-8, 10-1, AC-4, Ml-1 and the MOT variant are cDNA sequences and may, according to a further aspect of the present invention, be used as probes for the isolation and identification from genomic libraries of sequences upstream of the 5' region which contain the natural promoter region. The promoter region may then be identified, isolated and sequenced. According to a fifteenth aspect of the present invention there is provided a host cell transformed with a DNA construct comprising a polynucleotide sequence as described in sequences 2, 3 and 5 and Figure 19 or a vector described above comprising said polynucleotide sequence. The host cell is preferably a plant cell as described previously and the present invention extends also to whole plants having incorporated, preferably stably incorporated, into their genome a polynucleotide sequence, DNA construct or vector as described above, and to seeds, tubers and progeny of said plants. According to a sixteenth aspect of the present invention there is provided a DNA construct comprising a polynucleotide sequence comprising a switch promoter system operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct wherein when expression of said polynucleotide sequence is switched on from the switch promoter the resulting expression of said sense, antisense or partial sense sequence leads to down regulation of the expression of a further polynucleotide sequence encoding a transgene. In a seventeenth aspect the present invention provides a method of controlling the expression of a transgene comprising transforming a host cell with a DNA construct comprising a switch promoter system operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct, and a further DNA construct comprising a coding sequence coding for a transgene and controlling expression of the polynucleotide sequence from said switch promoter such that the resulting expression of the said sense, antisense or partial sense construct leads to down regulation of the expression of said transgene. As used herein the term "transgene" is used to denote a gene which is foreign or heterologous to the transformed host cell. In a preferred embodiment of the above aspects the present invention provides a DNA construct comprising the alcAJ alcR switch promoter operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct . The present invention also extends to a vector comprising said DNA constructs according to the above aspects of the invention. According to an eighteenth aspect of the present invention there is provided a host cell transformed with a DNA construct comprising a polynucleotide sequence comprising a switch promoter which may be switched on by the application of a chemical stimulus operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct wherein when expression of said polynucleotide sequence is switched on from the switch promoter the resulting expression of said sense, antisense or partial sense sequence leads to down regulation of the expression of a further polynucleotide sequence encoding a transgene. The host cell is preferably a plant cell as described previously and the present invention extends also to whole plants derived therefrom having incorporated, preferably stably incorporated, into their genome a polynucleotide sequence, DNA construct or vector as described above, and to seeds, tubers and progeny of said plants. The use of switch promoter systems to control expression of the sense, antisense or partial sense construct has many applications. Down-regulation of a gene, the expression of which gives rise to a lethal or inhibitory effect may be controlled using switchable sense, antisense or partial sense to facilitate the identification of suitable herbicide targets. Switchable down regulation using sense, antisense or partial sense sequences may also be used to identify mechanisms of cell ablation. The present invention therefore provides according to a nineteenth aspect a method of identifying a site which may be a suitable target for interaction with a herbicide comprising the steps of transforming a plant with a polynucleotide sequence comprising a first DNA sequence which is capable of affecting the expression of DNA at said target site wherein expression of said first DNA sequence is under the control of a switch promoter; controlling expression of said DNA sequence from said switch promoter such that the expression of the DNA coding for the herbicide target site is down regulated and determining the effects of said down regulation on the plant viability. The types of effects which would be monitored include the time period for which down regulation at the target site must be maintained and what level of down regulation is required and on the basis of the results obtained it can be decided whether the target site would be suitable as a target site for a herbicide. We have most unexpectedly found that the STLS-1 leaf promoter sequence acts as an enhancer of gene expression in tubers and the use of the STLS-1 sequence as an enhancer of gene expression in tubers forms a further aspect of the present invention. In a twentieth aspect the present invention therefore provides a method of enhancing gene expression in tubers comprising transforming a tuber plant cell with a polynucleotide sequence comprising a DNA sequence coding for all or part of the STLS-1 leaf promoter operably linked to a further promoter region. The STLS-1 leaf promoter is known in the art ( Eckes et al (1986) Mol. Gen. Genet. 205, 14-22) and is described in the accompanying examples. All or part of the DNA sequence coding for the STLS-1 leaf promoter may be used as an enhancer according to the invention. Active fragments of STLS-1 may be identified using techniques well known in the art such as restriction enzyme digestion followed by analysis of enhancement of gene expression of the fragments thus obtained. The STLS-1 promoter sequence may be inserted either upstream i.e. at the 5' end or downstream i.e. at the 3' end of the further promoter region. Insertion of the STLS-1 sequence upstream of the promoter region is especially preferred. In a particularly preferred embodiment of this aspect of the invention the STLS-1 sequence is inserted upstream of the 35S CaMV promoter. In a twenty-first aspect the present invention provides tubers, which are preferably potato tubers, derived from transgenic plants which do not sprout unless treated with a chemical inducer. According to a twenty-second aspect of the present invention, there is provided a polynucleotide sequence comprising all or part of at least one of the sequences depicted in Figures 25, 26 or 27 and polynucleotides having the same function as the sequence which is depicted in Figures 25, 26 or 27 which polynucleotide is complementary to one which still hybridises with the sequence comprised by that provided in Figures 25, 26 or 27 when incubated at or between low and high stringency conditions. Such sequences are preferably tuber specific promoters. According to a twenty-third aspect of the present invention, there is provided a method of controlling gene expression of a plant or a part thereof comprising transforming a plant cell with a chemically inducible plant gene expression cassette comprising a first promoter operatively linked to a regulator sequence derived from the ale R gene and a controllable promoter derived from the ale A gene promoter operatively linked to a target gene, wherein the controllable promoter is activated by the regulator protein in the presence of alcohol vapour thereby causing expression of the target gene. The present invention will now be described by way of the following non-limiting examples and with reference to the accompanying figures in which: Figure 1 : shows a diagram of the construction of plasmid pBIN-LN8. Figure 2: shows a schematic drawing of plasmid PPA-2. Figure 3 : shows a photograph of wild type (Desiree) and transgenic potato plants containing the phloem specific cytosolic invertase (genotype DLN-87, DLN-90 and DIN-30) following prolonged storage in the dark at room temperature. Figure 4 : shows western blot analysis of protein extracts from potato tubers of control plants and PPaII-2, -3, and -5 and PPaI-2 and PPaI-55 with an antibody raised to inorganic pyrophosphatase. Lanes 1 and 2 are samples from two independent tubers. Figure 5 : shows photographs of tubers harvested from wild type and transgenic plants after storage for five months at room temperature and in the dark. A: wild type control (Desiree); B: transgenic plant PPaII-2; C: transgenic plant PPaII-3; D: transgenic plant PPaII-5. Figure 6: shows: A: diagram of plasmid pJIT 166 B: diagram of pAGS/pUC GUS reporter gene construct Figure 7 : shows a map of plasmid AlcR/AGUS Figure 8 : Tissue culture grown potato plants were transferred into the greenhouse, following cultivation for 8 weeks in 2.5 1 pots. Ale expression was induced via watering the plants three times (day 0, 1 & 2) with 50 ml of a 5 % ethanol solution. On day 4 following the initial induction stolons and developing tubers were harvested and GUS activity was visualized using the histochemical staining procedure. 0 day, prior induction; 4 days, 4 days after initial induction shows histochemical detection of alc:GUS activity in stem, roots and stolons. 1 : non-induced stolon, 2: swelling tuber, 3: developing tuber and 4: mature tuber. Figure 9 : shows a photograph of potato tubers after histochemical detection of ale: GUS activity following ethanol vapour treatment. A: 0 days, B: 3 days, C: 7 days, D, untreated control, E, 7 days after treatment. Figure 10 : shows a map of plasmid pGSTTAK Figure 11 : shows a histogram analysis of GUS activity in fully developed leaves of GST-GUS transformed plants after cultivation for 14 days on MS-medium containing 0% | 0.4%02.0% Q and 10% 0 R-25788. Figure 12 : shows a diagram of the construction of plasmid SQ03. Figure 13 : shows a diagram of the construction of plasmid SQ-01. Figure 14 : shows a diagram of the construction of plasmid SQ-02. Figure 15 : shows a diagram of the cloning of potato ANT Figure 16 : shows accumulation of UBL-, GTP-binding-, AC4- and 16-8- specific transcripts during potato tuber storage at room temperature Figure 17 : shows accumulation of UBL-, GTP-binding-, 16-8-, and MOT- specific transcripts in different areas of sprouting tubers Figure 18: shows a diagram of the construction of an antisense MOT construct Figure 19 shows the DNA sequence encoding MOT isolated from potato Figure 20: shows sequence homology between the protein encoded by clone M-l-1 (MOT) and Panicum miliaceum mitochondrial oxoglutarate. Figure 21: shows the strategy for cloning the lac operator sequence into a RolC- invertase plasmid. Figure 22: shows the strategy for cloning Lac I into an Ale switch binary vector and ligation to RolCopINV. Figure 23: shows the isolation of the UBL-1 promoter by PCR. Figure 24: shows the isolation of the MOT- promoters by PCR. Figure 25: shows the UBL-1 promoter nucleic acid sequence. Figure 26: shows the MOT3 promoter nucleic acid sequence. Figure 27: shows the MOT6 promoter nucleic acid sequence. Figure 28: shows a CAT assay of ALC-CAT tobacco leaves from plants enclosed with an ethanol source for 24 hours. The numbers above the columns represent ng ethanol/ml headspace. Figure 29: shows the kinetics of CUS RNA transcript in 35S-Alc-GUS potato tubers after ethanol induction. The outer part refers to the part which is 1-3 mm beneath the skin of the potato tuber, the remaining part of the potato being referred to as the inner part. The induction was performed in 40 litres of plastic chamber tightly sealed with rubber for 1 week. The ethanol concentration was 0.02% gas phase (8 ml of 96% ethanol/401) and 20 μg of the total RNA was loaded onto each slot. Figure 30 shows the kinetics of GUS transcript and activity in 35S-Alc-GUS potato tubers induced by 1% ethanol. EXAMPLES I. Exemplification of sprout inhibition: 1. Inhibition of potato tuber sprouting via the expression of phloem-specific invertase 1.1. Construction of plasmid pBIN-RolC The rolC promoter from Agrobacteήum rhizogenes was cloned by polymerase chain reaction (PCR) following the instructions of the manufacturer (Perkin Elmer, Ueberlingen, Germany). The temperature profile of the PCR cycle (40 cycles) was as follows: 1 min at 95°C, 1 min at 45°C, and 2 min at 72°C. Plasmid DNA containing the rolC promoter was isolated from A. rhizogenes bearing the plasmid pABC002 (Schmϋlling et al., Plant Cell 1, 665-670 (1989)) using standard procedures (Sambrook et al, A Cloning Manual Cold Spring Harbor Laboratory Press 1989). Synthetic oligonucleotides were synthesised based on the published sequence of the rolC promoter fragment (Slightom et al., J. Biol Chem 261 (1) 108-121, 1986). The sequences of the primers were: 5"-ro/C primer d(GGAATTCGATACGAAAAAGGCAAGTGCC AGGGCC) and T-rolC primer d(CCCATG GTACCCCATAACTCGAA GCATCC). The amplified DNA was cloned into the PCR vector pCRlOOO™ (Invitrogen, Norwalk, CT). To exclude mutations of the amplified DNA during the PCR cycles, the clone was sequenced using the dideoxy method. The 1150-bp promoter fragment was subsequently cloned into a plant expression cassette pBfNAR (Hδfgen and Willmitzer Plant Sci. 66, 221-230 1990) by replacement of the 35S Cauliflower mosaic virus promoter sequence (Franck et al., Cell 21 285-294 (1980)) through the rolC promoter using 5' -restriction site of EcoRI and the 3 "-restriction site of Asp718 included in the PCR primers. The final construct is based on the binary vector pBinl9 (Bevan, Nucl Acid Res 12, 8711-8721 (1984)). The resulting plasmid contained the rolC promoter and the octopine synthase polyadenylation signal (Gielen et al, EMBO J 3, 835- 846 1984)). 1.2. Construction of plasmid pBLN-IN8 (Figure 1 ) To obtain a truncated version of the yeast Sue 2 gene PCR using the oligonucleotides 5'-Suc2 d(GAGCTGCAGATGGCAAACGAAACTAGCGATAGACCTTTGGTCACA) and 3 '-Suc2 d(GAGACTAGTTTATAACCTCTATTTTACTTCCCTTACTTGGAA) was applied to amplify the invertase gene from plasmid PI-3-INV (von Schaewen et al. EMBO J 9 3033-3044, (1990)). The PCR product was digested with Pstl/Spel and cloned into the Pstl/Xbal sites of plasmid YIP128A1 yielding plasmid 181A1-INV (Riesmeier et al., EMBO J. 11 4705-13 (1992)). To obtain BamHl sites at both ends of the invertase gene plasmid 181 A 1 -INV was digested with Pstl/BamHI and the invertase fragment was ligated into vector pBlueSK- yielding plasmid pBlue-Suc2A. Subsequently plasmid pBlue-Suc2A was digested with Spel/EcoRV, blunt ended with DNA polymerase and cloned into the Smal site of pBlueSK- yielding plasmid pBlue-Suc2B. Using plasmid pBlue-Suc2B the invertase gene was isolated as a BamHl fragment and cloned into the BamHl site of plasmid pBIN-RolC. The resulting plasmid (pBIN-IN8) contained the Suc2 gene (Nucleotide 849 to 2393) between the rolC promoter and the octopine synthase polyadenylation signal (Gielen et al., EMBO J. 3, 835-46, 1984). 1.3. Transformation of construct pBIN-IN8 Agrobacterium tumefaciens strain C58C1 containing pGV2260 (Deblaere et al., Nuc. Acid Res. 13, 4777-4788 (1989)) was transformed by direct transformation of variety Desiree by plasmid pBLN-IN8 as described by Hδfgen and Willmitzer (Nucl Acid Res. 16, 9877 (1988)). Potato transformation was achieved following the protocol of Rocha-Sosa et al. (EMBO J. 8, 23-29 (1989)). Primary screening for increased invertase activity was done in midribs of tissue-culture-grown regenerated plants. Three lines (DIN-87, 90 and 30) out of 75 independent transformants were selected for further analysis. For a detailed analysis, ten replicates of each preselected transformant were transferred into the green house for tuber production. 1.4. Invertase activity Invertase assay. Plant tissue, quickly frozen in liquid nitrogen, was homogenised in extraction buffer (50 mM 4-(2-hydroxyethyl)-l-piperazineethane sulfonic acid (Hepes)- KOH, pH 7.4; 5 mM MgCtø; 1 mM EDTA; 1 mM ethylene glycol-bis(b-aminoethylether)- N,N,N',N'-tetraacetic acid (EGTA); 1 mM phenyl-methylsulfonyl-fluoride (PMSF); 5 mM dithiothreitol (DTT); 0.1% Triton X-100, 10% glycerol) and centrifuged (5 min, 4°C, 9000 g, Biofuge 13; Heraeus, Hanau, Germany). For assaying neutral invertase the reaction mixture contained 20 mM Hepes-KOH pH 7.5, 100 mM sucrose and 10-30 μl of the protein extract in a final volume of 100 μl. Incubation was carried out at 30°C for 30-60 minutes and stopped at 95°C for 3 minutes. Blanks had the same reaction mixture but were heat inactivated without incubation. The determination of glucose and fructose was as described in Stitt et al. (Methods Enzymol. 174, 518-522 (1989)). For assaying soluble acid invertase the reaction mixture contained 20 mM sodium acetate pH 4.7, 100 mM sucrose and 10-30 μl of the protein extract in a final volume of 100 μl. Incubation was carried out at 30°C for 30- 90 minutes. To neutralise the reaction mixture before stopping the reaction at 95°C for 3 minutes 10 μl of 1 M sodium phosphate pH 7.2 was added. Blanks had the same reaction mixture but were heat inactivated without incubation. Following harvest tubers of transformed and untransformed potato plants were stored for 5 months at 20°C. Subsequently neutral and acidic invertase activity was determined in tuber slices. The result is shown in Table 1. Table 1 : Invertase activity in potato tubers stored for 5 month at 20°C. genotype neutral invertase soluble acidic invertase Control 32.7 ± 4.2 18.0 ± 1.3 D DIINN--8877 1 11155..33 ±± 66..11 141.2 ± 8.8 DIN-90 93.9 ± 4.7 126.0 ± 6.2 DIN-30 121.5 ± 8.4 174.8 ± 16.5 Mean values are given ± standard deviation (n=4). Invertase activity is presented in nmol gFW^mhr 1 . Control is wild type Desiree. 1.5. Impact of invertase on sugar accumulation in potato tubers Determination of soluble sugars. Tubers were harvested and tuber slices (60-70 mg fresh weight, 0.1 cm 3 average volume) were immediately frozen in liquid nitrogen. The slices were extracted with 1 ml 80% ethanol (10 mM Hepes-KOH, pH 7.4) at 80°C for 1-2 h. The supernatant was used for the determination of glucose, fructose and sucrose as described in Stitt et al. (1989). The pellet was extracted a second time, washed in water, and dried. Determination of starch content was done using a starch determination kit (Boehringer Mannheim). The results are shown in Table 2. Table 2: Carbohydrate composition of potato tubers expressing cytosolic yeast invertase under control of the RolC promoter. Genotype Fructose Glucose Sucrose Starch Control 0.9 ± 0.1 6.2 ±0.2 8.7 ± 0.4 652 ± 15 DLN-30 0.3 ± 0.1 8.7 ± 1.0 2.1 ± 0.2 604 ± 19 DIN-87 0.8 ± 0.1 6.5 ± 0.4 3.1 ± 0.2 753 ± 26 DIN-90 0.8 ± 0.01 3.1 ± 0.6 3.5 ± 0.1 903 ± 39 Mean values are given ± standard error (n=12, control; n=4, transgenic). Sugar content is presented as μmol hexoses gFW" 1 . Control is wild type Desiree 1.6. Yield Potato plants were grown in a greenhouse at 60% relative humidity in a 16 h light (22°C) and 8 h dark (15°C) cycle (irradiance 300 μmol nr 2 s" 1 ). To estimate the impact of phloem-specific cytosolic yeast-derived invertase on tuber fresh weight and tuber number ten plants each genotype were cultivated in 2 1 pots. As shown in Table 3, total fresh weight and tuber number of the transgenic plants is indistinguishable from wildtype. Table 3: Tuber yield of invertase expressing potato plants Genotype Tuber fresh ' weight Tuber number Control 118.3 = 1.1 15 ± 0.01 DIN-87 116.5 ± 6.1 11 ± 1.9 DIN-90 121.1 ± 0.2 12 ± 1.9 DIN-30 106 ± 10.5 13.5 ± 2.8 Mean values are given ± standard deviation (n=10). Tuber fresh weight is presented in g. Control is wild type Desiree 1.7. Sprout inhibition of transgenic plants. To investigate the impact of phloem-specific cytosolic invertase on tuber sprouting harvested tubers of transformed and wildtype plants were stored for a prolonged time in the dark at room temperature. Wildtype Desiree tubers started to sprout after 5 to 6 months whereas tubers of transgenic plants did not show any visible sign of sprouting. Even after one year of storage tubers of transgenic plants did not develop any vital sprout (Figure 3). Thus, expression of phloem-specific invertase leads to a complete inhibition of potato tuber sprouting. 2. Inhibition of tuber sprouting via expression of E. coli inorganic pyrophosphatase 2.1. Construction of plasmid PPA-2 and potato transformation (Figure 2 ) The 1600 bp promoter fragment of the STLS-1 gene (Eckes et al., Mol. Gen. Genet. 205, 14-22 (1986)) was isolated as a EcoRI-Ba HI fragment from plasmid 1600-CAT (Stockhaus et al., 1987). After removal of the overlapping nucleotides the fragment was cloned into the blunted EcoRI site of the chimeric ppa gene described in Sonnewald (Plant J. 2, 571-581 (1992)). The final construct containing the STLS-1 promoter/enhancer, the 35S CaMV promoter, the TMV-U1 translational enhancer, the E. coli ppa coding region and the octopine synthase polyadenylation signal was cloned as a EcoRI-Hindlll fragment into the binary vector Binl9 (Bevan, 1984 J. loc cit). Direct transformation of Agrobacterium tumefaciens strain C58C1 :pGV2260 was done as described by Hofgen and Willmitzer (Nucl Acid Res.16 9877 (1988)). Potato transformation using Agrobacterium-mediated gene transfer was performed as described by Rocha-Sosa et al. (EMBO J. 8 23-29 (1989)). Following Agrobacterium mediated gene transfer forty independent transformed plants were analysed for the presence of the PPase protein using immunoblotting. Three plants (PPaII-2, 3 and 5) with the highest amount of PPase protein were selected for further analysis. To compare the promoter strength of the chimeric 35S CaMV promoter (PPall) and the unmodified 35S CaMV promoter (PPal) protein extracts from potato tubers were analysed by western blotting. As shown in Figure 4, the amount of the PPase protein, detectable in protein extracts from growing PPall tubers, is significantly higher as compared to the PPal control. The same results were obtained in tubers stored for three and twelve months at room temperature. This analysis compared the highest expressing lines from the PPal and PPall populations where 70 independent transformants were selected for PPal and 40 for PPall. It is clear from this analysis that the STL1 promoter fragment enhances tuber expression of inorganic pyrophosphatase. The expression of the E. coli inorganic pyrophosphatase was paralleled by an increase in pyrophosphatase activity measured in protein extracts from PPall tubers (Table 4). Depending on the amount of pyrophosphatase activity the pyrophosphate content decreased up to two-fold (Table 4). Table 4: Elevated cytosolic inorganic pyrophosphatase leads to reduced PPi accumulation in tubers of PPall transformants. Genotype Pyrophosphatase activity Pyrophosphate [μmol g FW _1 minute" 1 ] [nmol g FW _ 1 ] Control 3600 ± 410 2.4 ± 0.2 PPaII-2 5600 ± 150 1.4 ± 0.2 PPaII-3 6200 ± 220 1.2 ± 0.3 PPaII-5 8500 ± 220 1.1 ± 0.1 Tubers were harvested from plants grown for 150 days in the greenhouse. The results are mean values ± SD (n = 3 for wildtype and n = 4 for transgenic plants) of three tubers from three different wildtype plants and two to four tubers each PPall plant. 2.2. Immunoblot analysis Following separation on 12.5% SDS polyacrylamide gels (Laemmli, 1970), proteins were transferred onto nitrocellulose membranes (Millipore, Bradford, Mass., USA) using a semi-dry electroblotting apparatus (Multiphore II; LKB, Bromma, Sweden). Incubation with anti-PPase polyclonal antibodies (Lerchl et al., Plant Cell 7 259-270 (1995)) in a 1 : 1000 dilution was for 90 minutes at room temperature. Immunodetection of the antigen was done using the biotin-streptavidin system from Amersham Buchler with rabbit biotinylated species-specific whole antibodies (from donkey) and streptavidin-biotinylated horse-radish peroxidase. 2.3. Pyrophosphatase activity assay To measure pyrophosphatase (PPase) activity 100-200 mg potato tuber slices were homogenised in 0.5 ml 100 mM 4-(2-hydroxyethyl)-l-piperazineethanesulfonic acid (HEPES)-KOH (pH 7.5), 2 mM Mg2Cl, 1 mM EDTA, 1 mM EGTA, 5 mM mercaptoethanol. After centrifugation (10 minutes, 13 000 rpm at 4°C) 20μl of the supernatant was assayed in 160 μl 50 mM Tris-HCL (pH 8.0), 16 mM MgSO4 and 100 mM KC1 for PPase activity. Following addition of 20 μl 50 mM NaPPi the reaction was carried out for 20 minutes at 30°C. The reaction was stopped by addition of 20 μl IM citrate and the release of inorganic phosphate was assayed as in Heinonen and Lathi (Anal Biochem 113, 313-317 (1981)). The assay was linear with time and amount of extract. 2.4. Determination of inorganic pyrophosphate in tuber tissue To measure pyrophosphate 200 - 300 mg of tuber tissue was frozen in liquid nitrogen. Frozen material was subsequently homogenised to a fine powder in liquid nitrogen in a mortar standing on powdered dry ice (solid CO2). A 15 ml aliquot of 16 % trichloroacetic acid (TCA) in diethylether (v/v), precooled to the temperature of dry ice, was added and the sample further homogenised. After leaving the homogenate for 20 minutes on dry ice, 0.8 ml of 16 % TCA in water (v/v) containing 5 mM NaF was added. The mixture was warmed to 4°C and left for 3 hours. Subsequently the homogenate was extracted four times with diethylether and neutralised with KOH/triethanolamine as in Weiner et al. (Biochem Biophys Acta 893, 13-21 (1987)). All mortars and materials were prewashed for 12 hours in 2 N HC1, and pseudoextracts were prepared in parallel to check that the reagents and apparatus were not contaminated with pyrophosphate. efore assaying for pyrophosphate content 400 μl of extract was added to 400 μl of cation exchanger (Serva, Heidelberg, FRG; Dowex AG 50 x 8, 100-200 Mesh, preequilibrated with 2 N HC1, brought to pH 5 with water, and then dried for 12 hours at room temperature), mixed for 20 seconds, and centrifuged to remove compounds in the extract which interfere with the metabolite assay. Pyrophosphate was assayed photometrically as in Weiner et al. (1987). The reliability of the extraction and assay was checked by adding a small representative amount (two- to threefold the endogenous content) of pyrophosphate to the plant material in the killed mixture of TCA and diethylether. 2.5. Yield Potato plants were grown in a greenhouse at 60% relative humidity in a 16 h light (22°C) and 8 h dark (15°C) cycle (irradiance 300 μmol πr 2 s _1 ). To estimate the impact of the E.coli inorganic pyrophosphatase on tuber fresh weight and tuber number five plants each genotype were cultivated in 2 1 pots. Total tuber fresh weight of PPall plants was unaltered as compared to wildtype controls (Table 5). Table 5: Influence of E.coli inorganic pyrophosphatase on potato tuber development. The tubers were harvested from plants which had been growing in the green house for 150 days. The results are means of five individual plants each genotype. Genotype Tuber fresh weight [g] Tuber number Control 89-148 12 ± 0.6 PPaII-3 99-139 19 ± 1.7 P PPPaaIIII--55 1 11100--116677 21 ± 4.0 PPaII-2 89-192 19 ± 0.5 of expression in the PPal transgenic plants was not sufficient to prevent sprouting. 2.6. Sprout inhibition of transgenic plants . Tubers harvested from wildtype plants started to sprout after five to six months of storage, whereas PPall tubers did not develop any visible sprout (Figure 5). While sprout development of wildtype tubers continued, there was still no indication of sprouting in PPall tubers after twelve months of storage. Even after a prolonged storage of two years, PPall tubers did not sprout. Treatment of potato tubers with gibberellic acid, ethephon, higher- and lower temperatures or light did not induce sprouting of PPall tubers. The low level II. Exemplification of inducible gene expression in potato tubers 3. Ethanol inducible gene expression 3.1. Construction of plasmid Alc:GUS The source of the GUS gene was the pUC based plasmid pJIT166 (Figure 6). A fragment containing the GUS coding region and CaMV35S terminator, from pJIT166 was cloned into pACN/pUC vector using Sail and Bglll. Bglll cuts three times in the CaMV35S terminator. The first cut occurs 250 bases beyond the end of the GUS gene. Although this only takes a small part of the terminator the fragment contains all necessary sequences required for the termination of transcription. The Sall-Bglll digest of pJIT166 yielded a 1.8 kbp fragment containing the GUS gene plus the truncated CaMV35S terminator. This fragment was cloned into pACN/pUC digested with Sail and Bglll to remove the CAT gene and the nos terminator leaving a Sail overhang at the 5' end behind the alcA promoter and a Bglll overhang at the 3' end of the linearised vector. The fragment containing the GUS gene and the CaMV35S terminator was ligated into the linearised pUC vector containing the ale A promoter using standard protocols. The final step in the cloning procedure was to clone the alcA-GUS-35St fragment into pSRN-ACN/BinN19, in place of the alcA-CAT-nos fragment. The resulting Bin 19 vector would then contain all the components of the ale regulon but with the GUS reporter. The alcA-CAT-nos fragment was excised from pSRN-ACN/Binl9 vector with a Hindlll digestion. The remaining 16.1 kbp fragment, which is the Binl9 vector still with the 35S-alcR-nos region, was extracted from the gel by electro-elution. The alcA-GUS- 35 St fragment was then excised with a Hindlll Xmnl double digest of pAGS/pUC. The restriction enzyme Xmnl cuts approximately 850 bp off the pUC19 vector giving separation and allowing the removal of the alcA-GUS-35St fragment. The alcA-GUS-35St fragment was then cloned into the vacant Hindlll site in pSRN/Binl 9. The fragment was orientated using restriction mapping and then sequenced to confirm that they contained the correct sequences. A map of plasmid AlcR/AGUS is provided in Figure 7. 3.2. Transformation of construct Direct transformation of Agrobacterium tumefaciens strain C58Cl:pGV2260 was done as described by Hofgen and Willmitzer (1988)( J. loc cit). Potato transformation (Solara) using Agrobacterium -mediated gene transfer was performed as described by Rocha-Sosa et al. (1989) (J. loc cit). Following Agrobacterium mediated gene transfer 100 independent transformed plants were selected. To test inducibility of the GUS activity shoots of transgenic plants were duplicated in tissue culture. Following root formation one set of plants was transferred into the greenhouse. Two weeks after transfer into the greenhouse ethanol inducibility was assayed by adding 50 ml of a 5 % ethanol solution to the root system of the potato plants. Subsequently GUS activity was visualised using the histochemical detection system. Following ethanol induction GUS activity was visible in all tissues tested (sink- and source leaves, stem, roots and stolons). As shown in Figure 8 GUS activity was highly inducible in developing and mature tubers. There was no detectable GUS activity in any organ in uninduced potato plants. In order to investigate the sensitivity of the Ale-switch to ethanol vapour an experimental system was used where an Alc-CAT(chloramphenical acetyl transferase) tobacco plant (CaMV35S-AlcR-nos, AlcA-CAT-nos; Caddick et al, 1998) was enclosed in a sealed container with a pot of ethanol of a particular concentration to act as a source of ethanol vapour. Headspace and leaf samples were taken after 24 hours. Absolute amounts of ethanol in the headspace samples was quantified by relating the ethanol peak area obtained after injection using a gas-tight syringe into a gas chromatography machine with a mass spectrometry detector to that with an ethanol standard solution. Total CAT expression levels in leaves were determined by CAT ELISA. CAT expression in tobacco plants enclosed with ethanol solutions of 5, 1, 0.1 and 0.05 % were relatively constant but dropped dramatically with 0.01, 0.005 and 0.001 % ethanol solutions (see Figure 28). Relating the levels of CAT activity to ethanol vapour concentrations in the container, the threshold of Ale-switch activation was seen at an ethanol concentration of between 72 and 21 ng/ml air. To further study the inducibility of GUS in stored potato tubers four GUS positive transgenic lines were selected for a detailed analysis. After multiplication in tissue culture 5 plants of each genotype were transferred to the green house for tuber production. Following harvest tubers were placed in a sealed glass container containing 3MM paper soaked with a 5 % ethanol solution. To prove that ethanol induction would be efficient throughout the whole potato tuber slices were taken at different times following ethanol induction and GUS activity was visualised using the histochemical detection method. As shown in Figure 9 homogenous induction of GUS activity was found in intact potato tubers. The use of ethanol vapour to activate the Ale-switch was investigated in Alc-GUS potato tubers (CaMV35S-AlcR-nos, AlcA-GUS-nos). The kinetics of GUS RNA transcript accumulation was determined by northern analysis. Potato tubers were enclosed with an ethanol source for 3, 6, 9, 12, 24, 48 hours and 1 week time points, the ethanol source removed and samples subsequently taken at 2, 3 and 4 week time-points. By varying the concentration of ethanol used for induction in the enclosed system, the timecourse of GUS transcript accumulation can be altered. Using 8ml of absolute ethanol in a 40 litre container low levels of GUS transcript can first be detected at 6 h in the outer 1 -3 mm below the tuber skin and at 12 h 3 mm or more below the skin surface (see Figure 29). Maximal levels of transcript were detected at 24 h with transcript persisting until 4 weeks. In contrast, using a 5 % ethanol solution to generate a lower ethanol vapour concentration transcript is first detected at 1 week. By keeping the a constant ethanol source GUS transcript was detected at high levels through-out the course of the experiment (last time-point 3 months) (see Figure 30). An extension of these ethanol vapour studies was to investigate Ale-switch induction in tomato fruit. Using a 5 % ethanol solution enclosed in a 2.6 1 container with Alc-GUS tomato fruit (CaMV35S-AlcR-nos, AlcA-GUS-nos), significant GUS staining was observed in the walls of the pericarp originating from the stig in fruit after 4 weeks of ethanol exposure. Tomato fruit were sliced, washed briefly in 50 mM sodium phosphate buffer, pH. 7.0 and incubated in staining buffer (50 mM sodium phosphate buffer, pH. 7.0, 50 uM potassium ferricyanide, 50 uM potassium ferrocyanide, 2 % triton XI 00, 20 % methanol and 1 mM 5-bromo-4-chloro-3-indolyl-B-D-glucoronide) as required. Staining was stopped by performing 100 % and 70 % ethanol washes and the fruit slices stored in 70 % ethanol at 4 °C. 3.3. Fluorometric determination of GUS activity The fluorometric determination of GUS activity was carried out as follows: Tuber slices harvested after the indicated times following ethanol induction were frozen in liquid nitrogen. Subsequently tuber tissue was homogenised in 50 mM NaHPO4 (pH 7.0), 10 mM mercaptoethanol, 10 mM EDTA, 0.1 % sodium lauryl sarcosine, 0.1 % Triton X-100. The homogenate was centrifuged for 10 minutes at 13.000 rpm at 4°C, the cleared supernatant was collected and used for the determination of protein content and GUS activity. For fluorometric detection 20 μl of extract (diluted to a proper concentration) was added to 480 μl GUS assay buffer (2 mM MUG in extraction buffer) and incubated for 30 minutes at 37°C. Thereafter 50 μl of the reaction mixture was transferred to 1950 μl stop solution. The fluorimetric signal of each sample was determined with a TKO 100 mini-fluorometer (excitation at 365 nm, emission at 455 nm). From the initial slope of the curve obtained by plotting the fluorometric value against time enzyme activity was calculated. Heat inactivated extract served as controls. The activity values were normalised to the protein concentration of each extract. 3.4. Histochemical detection of GUS activity For histochemical detection of GUS activity tissue samples were incubated in X-gluc buffer (25 mM sodium phosphate buffer (pH 7.2), 25 mM potassium phosphate (pH 7.2), 0.1 % Triton X-100, 1 mM X-gluc). Brief vacuum infiltration (30 seconds) was used to support penetration of the substrate into the plant tissue. Subsequently the material was incubated at 37°C for 3 to 24 hours and rinsed with water before photography. Photosynthetic tissue were bleached with ethanol. Microscopic analysis was performed using an Wild Makroskop M420 equipped with a Wild MPS46 photoautomat. III. Safener inducible gene expression in potato plants 4.1. Construction of GST:GUS plasmid Standard recombinant DNA methods were adopted in the construction of plasmid vectors. A reporter gene construct containing a GST-273.8 kb EcoRl-Nde I 5' flanking region from pGlE7 was blunted ended and ligated into the Sma I site of the Agrobacterium Ti vector pBHOl . The Nde I site, which lies at the predicted translation start codon of GST-27 was destroyed after blunting. This formed a convenient point for fusion with the E. coli UidA gene, encoding b-glucuronidase (GUS) in pBHOl. The structure of the resultant chimeric reporter gene construct pGSTTAK was verified by restriction and sequence analysis. A map of plasmid pGSTTAK is provided in Figure 10. 4.2. Transformation of construct and test of inducibility Using plasmid pGST::GUS direct transformation of Agrobacterium tumefaciens strain C58Cl:pGV2260 was done as described by Hδfgen and Willmitzer (1988) (J. loc cit). Potato transformation (Solara) using Agrobacterium-mediated gene transfer was performed as described by Rocha-Sosa et al. (1989) (J. loc cit). Following Agrobacterium mediated gene transfer 100 kanamycin resistant regenerated shoots were selected. Safener inducibility was tested by transferring stem cuttings of GST::GUS transformed potato plants on MS medium containing 0, 0.4, 2.0 and 10 %o R- 25788 (final concentration). Following cultivation for 14 days fully developed leaves were harvested and GUS activity determined. As shown in Figure 11, a 3 to 20 fold increase in GUS activity could be obtained following safener induction. IV. Inducible repression of the expression of target genes 5. Inducible co-suppression 5.1. Construction of chimeric gene for inducible FNR co-suppression To achieve ethanol inducible co-suppression of NADP-ferredoxine oxidoreductase (FNR) a ca. 450 base pair 3 '-fragment (Seq. 1) of a tobacco FNR cDNA was fused to the alcA promoter in the sense orientation yielding plasmid SQ03. The cloning strategy is illustrated in Figure 12. Direct transformation of Agrobacterium tumefaciens strain C58Cl:pGV2260 was done as described by Hδfgen and WiUmitzer (1988) (J. loc cit). Tobacco transformation (Samsun) using Agrobacterium -mediated gene transfer was performed as described by Rosahl et al. (EMBO J 6, 23-29, (1987)). ollowing Agrobacterium mediated gene transfer 100 independent transformed plants were selected. Seq. 1 : Total number of bases 423 ττττττττττ ττττττττττ ττττττττττ ττττττττττ TTC CCAAAAA ATGAAATTAA AATTTCAAAG GAAAAATTTA CCTATCTACA TGGATGCAGG GGGAGAGAAG CATAAAGTTG GCTCATATTT GTACAAAGAA AAGTAAAAAT ATTTAGTAGA CTTCAACATT CCATTGCTCT GCCTTCTTCA ATTGCTTCTT GTAGTCCGCC CAGACAATAC CATCTCTTTC AGCAAGAGCA GACATAATTT CATCAATTCC CTGCTCCATG CCCTTGAGTC CACACATGTA GATGAAGGTG TTGTCTTTTT GGAGCAAAGT CCATAGTTCT TCAGCATATT GAGCCATTCT GGTTTGAATG TACATCTTTT CACCCTTTCC GTTCGTTTGC TCTCTGCTCA CAGCAAAGTC CAATCTGAAG TTT-3' V. Inducible antisense repression of heterologous genes As described in section I expression of cytosolic invertase and inorganic pyrophosphatase can lead to a non-sprouting phenotype when suitable promoters are used to drive the expression of the respective gene. To achieve inducible reversion of the non- sprouting phenotype a strategy for the inducible antisense of the heterologous gene was applied. 6. Inducible antisense repression of pyrophosphatase expression 6.1. Construction of plasmid SQ01 As shown in Figure 5 high level expression of E. coli inorganic pyrophosphatase leads to a non-sprouting phenotype of harvested potato tubers. To chemically control the expression of E. coli inorganic pyrophosphatase plasmid SQ01 was designed. The plasmid contains three chimeric genes: (a) the alcR gene under control of the 35S CaMV promoter, (b) the ppa gene under control of the enhanced 35S CaMV promoter and (c) the ppa gene in the antisense orientation under control of the ale A promoter. The construction of plasmid SQ01 is shown in Figure 13. 6.2. Plant Transformation Direct transformation of Agrobacterium tumefaciens strain C58C1 :pGV2260 was done as described by Hδfgen and WiUmitzer (1988) (J. loc cit). Potato transformation (Solara) and tobacco (Samsun) using Agrobacterium -mediated gene transfer was performed as described by Rocha-Sosa et al. (1989) (J. loc cit) and as described by Rosahl et al. (1987) (J. loc cit). Following Agrobacterium mediated gene transfer 100 independent transformed plants were selected. 6.3. Immunological detection of ppa The successful transformation was tested by the immunological detection of the E. coli pyrophosphatase protein in leaf extracts of tissue culture grown potato plants. Based on the initial screening 15 independent transgenic plants could be identified. Following duplication in tissue culture pyrophosphates expressing transgenic potato plants were transferred into the green house for tuber formation. 7. Inducible antisense repression of invertase expression 7.1. Construction of plasmid SQ02 As shown in Figure 3 phloem-specific expression of cytosolic yeast-derived invertase leads to a non-sprouting phenotype of harvested potato tubers. To chemically control the expression of yeast invertase plasmid SQ02 was created. The plasmid contains three chimeric genes: (a) the alcR gene under control of the 35S CaMV promoter, (b) the truncated suc2 gene encoding the mature invertase protein under control of the rolC promoter and (c) the suc2 gene in the antisense orientation under control of the ale A promoter. The construction of plasmid SQ02 is shown in Figure 14. 7.2. Plant Transformation Direct transformation of Agrobacterium tumefaciens strain C58C1 :pGV2260 was done as described by Hδfgen and WiUmitzer (1988)(J. loc cit). Potato transformation (Solara) and tobacco (Samsun) using Agrobacterium -mediated gene transfer was performed as described by Rocha-Sosa et al. (1989)(J. loc cit) and as described by Rosahl et al. (1987) (J. loc cit). Following Agrobacterium mediated gene transfer 100 independent transformed plants were selected. 7.3. Invertase activity The successful transformation was tested by the detection of invertase activity in SDS PAA-gels as described in von Schaewen et al. (EMBO J. 9, 3033-3044 (1990)). To this end protein extracts were prepared from midribs of tissue culture grown potato plants. Following separation of the protein extracts in 12.5% SDS PAA gels the gel was washed in 100 mM Na-Acetate buffer pH 5.0 for 30 minutes. Subsequently the gel was incubated in 100 mM Na- Acetate buffer containing 100 mM Sucrose at 37°C for 1 hour. After a brief wash with distilled water invertase activity was visualised via the detection of liberated reducing sugars (glucose and fructose). Hexoses were detected by boiling the gel in 0.1% 2,3,5- Triphenyltetrazoliumchlorid in 0.5N NaOH for 2-5 minutes. Invertase activity became visible due to the formation of an intense red colour. Based on the initial screening 18 independent transgenic plants could be identified. Following duplication in tissue culture invertase expressing transgenic potato plants were transferred into the green house for tuber formation. VI. Use of operator/ repressor system to repress heterologous genes 8. Use of Lac operator/ repressor system with the rolC promoter, the yeast-derived invertase gene and the Ale switch. 8.1. Cloning of lad into ALC switch binary vector. As can be seen from Figure 22, the lacl-nos region was excised from a 35S-LacI-nos plasmid with BamHl /Hindlll and cloned into a BamHl /Hindlll digested pMSC2 vector. This vector has a Pstl site a few bases 5' to the BamHl site, so a Pstl digest removed the lad coding region. This was then cloned into a pstl digested pACN vector (AlcA-cat-nos), replacing the AlcA gene with the lad gene, to give a pALN vector (AlcA- lacl-nos). The ALN region was removed from this with a Hindlll digest and cloned into a Hindlll digested binary SRNACN (35S-AlcR-Nos-AlcA-Cat-Nos) vector, replacing the ACN with the ALN cassette. 8.2. Cloning the lad operator into RolC-invertase Two oligonucleotides were synthesised with Ba Hl and Asp718 restriction sites SC24: TTGGTACCAATTGTGAGCGCTCACAATTGGATCCTT SC25 : AAGGATCCAATTGTGAGCGCTCACAATTGGTACCAA. lOuM of both oligonucleotides were annealed by boiling in a water bath in the presence of 20mMTris.Cl (pH8.4) 50mM KC1 and 1.5mM MgCl 2 for 5 minutes before cooling down to 30°C over approximately one hour, followed by 5 minutes on ice. The annealed oligonucleotides were digested with BamHl and Asp718, and the restriction enzymes inactivated by phenol extraction and ethanol precipitation. The fragments were ligated into BamHl and Asp718 cut pUC19 to give pUC-/αcO. The plasmid was confirmed by sequencing. The OCS terminator was removed from the BINAR plasmid and cloned into the Sail and Hindlll restriction sites of plasmid pUC-/αcO creating the plasmid pUC-/αcO-ocs. The RolC promoter was inserted with EcoRI and Asp718 (Kpnl) to give the plasmid pUC- RoIC-/ cO-ocs. The yeast derived invertase was inserted into the BamHl site of pUC- RoIC-/αcO-ocs resulting in the plasmid pUC-RolC-/αcO-INV-ocs. Figure 21 shows the cloning strategy for this plasmid. 8.3.Ligation of above two components to give the final binary vector The RolCopINVocs cassette is on a Hindlll fragment (using the 865bp RolC promoter) and was ligated to a Hindlll digested binary SRNAlacI in a three-way ligation, to give the final construct of 35S-AlcR-nos-AlcA-/ cI-nos-RoIC-op-invertase-ocs. VII. Additional targets Based on known biochemical steps involved in potato tuber sprouting we have identified several additional targets which may be used to create genetically engineered non- sprouting potato tubers. Besides others, respiratory enzymes or membrane proteins involved in the mitochondrial export of metabolites are promising. One of these candidates is the mitochondrial ATP/ADP translocator and a second malate oxoglutarate translocator. 9. Genes involved in mitochondrial function 9.1. Cloning of ATP/ADP translocator (ANT) and construction of a chimeric antisense gene Based on a published sequence of potato ADP/ATP translocator (Emmermann et al. (1991) Curr. Genet. 20, 405-410) oligonucleotides were designed to allow PCR- amplification of an internal ANT-fragment (see Figure 15). The following PCR-primers were used: 5 '-ANT primer: 5'- AACGGATCCATGGCAGATATGAACCAGC -3 '; 3'-ANT primer: 5 ' - TTGGATCCTT ACAACACACCCGCCCAGGC -3'. To optimise subsequent cloning of the ANT-fragment into plant expression vectors BamHl sites were included in both PCR primers. As template reverse transcript mRNA isolated from growing potato tubers was used. RNA isolation was done according to Logemann et al. (1987; Anal. Biochem., 163, 16-20). Single strand cDNA was synthesised using M-MLV superscript reverse transcriptase according to the instructions of the manufacturer (Gibco, BRL). The temperature profile of the PCR cycle (40 cycles) was as follows: 1 min at 95°C, 1 min at 45°C, and 2 min at 72°C. The amplified DNA was cloned into the PCR vector pCRl 000™ (Invitrogen, Norwalk, CT). To exclude mutations of the amplified DNA during the PCR cycles, the clone was sequenced using the dideoxy method. The 1120-bp ANT fragment was subsequently cloned into a plant expression cassette pBLNAR (Hδfgen and WiUmitzer Plant Sci. 66 221-230 (1990)) in the antisense orientation (Fig. 15). 9.2 Cloning of Mitochondrial Oxoglutarate Translocator (MOT) A cDNA fragment encoding MOT was isolated using the methods described in Section 9.1. Northern analysis on Figure 17 shows the MOT mRNA expression is highest when RNA is extracted immediately below the tuber sprout. This region corresponds to high metabolic activity. An antisense downregulation construct was prepared by amplifying the MOT fragment essentially as described above in section 8.1 for ANT but using the primers shown in Figure 18. The BamHI/Sall PCR fragment was cloned into Bam/Sal cut pBluescript SK. To exclude mutations of the amplified DNA during the PCR cycles, the clone was sequenced using the dideoxy method. An Asp718/BamHI fragment was excised from the pBluescript vector described and cloned into BamHl/ Asp718 cut pBinAR. This yielded a plant transformation cassette containing the 35S CaMV promoter driving MOT in an antisense orientation. 9.3. Transformation Direct transformation of Agrobacterium tumefaciens strain C58C1 :pGV2260 was done as described by Hδfgen and WiUmitzer (1988) (J. loc cit.). Potato transformation using Agrobacterium -mediated gene transfer was performed as described by Rocha-Sosa et al. (1989)(J. loc cit). Following Agrobacterium mediated gene transfer 70 independent transformed plants were selected. 10. Genes induced during potato tuber storage 10.1. Isolation of genes induced during tuber storage 10.1.1. Differential display To gain insight into molecular changes occurring during the transition of growing to sprouting tubers the differential display technique was used. To this end total RNA was isolated from growing and stored potato tubers (Desiree). Following DNasel digestion 5 μg of total RNA was reverse transcript using M-MLV superscript reverse transcriptase (Gibco, BRL) yielding single strand cDNA templates. Subsequently, PCR amplification of the prepared cDNA templates was carried out in the presence of (α- 35 S)dATP using oligo- d(T) 11 -XN and 100 different RAPD primers. The use of the following RAPD-primers led to the isolation of source tuber-specific cDNA fragments: 5'- AAGCGACCTG -3'; 5'- GTTGGTGGCT -3'; 5'- ACGGGACCTG -3'. The temperature profile of the PCR cycle (40 cycles) was as follows: 30 seconds at 94°C, 1 min at 42°C, and 30 seconds at 72°C. The amplified DNA was denatured for 5 minutes in formamide buffer at 94°C and loaded onto a PAA-gel (6% acrylamide, 0.3% bisacrylamide, 7 M urea in TBE buffer). Separation of the cDNA fragments was done at 1.75 KV, 130 mA for 3 hours. Following separation the gel was dried at 80°C and radioactive labelled cDNA fragments were visualised via autoradiography using Kodak X- OMAT X-ray films. Exposure time ranged from 2 to 5 days. Comparison between cDNA fragments amplified from growing or sprouting tuber templates allowed the detection of cDNA fragments being exclusively present in sprouting potato tubers. Sprouting tuber- specific cDNA fragments were subsequently eluted from the PAAG and reamplified using the respective PCR primers. The reamplified cDNA fragments were subsequently cloned into the PGEMT vector (Promega). The size of the amplified cDNA fragments varied between 200 and 450 base pairs. 10.1.2. Northern blot analysis of genes induced during tuber storage To verify that the isolated cDNA fragments are induced in stored potato tubers total RNA of growing and 1, 7, 14, 21, 30, 60, 90, 120, 150 and 180 days stored potato tubers was isolated, separated in 1.5 % formaldehyde (15% v/v) containing agarose gels and probed for the presence of the respective transcripts following transfer of the RNA onto nylon membranes. As shown in Figure 16 the transcripts of 4 isolated clones (16-3, 10-1, AC4 and 16-8) accumulate during potato tuber storage. 10.1.4. Construction of cDNA library To obtain full size cDNA clones encoding M-l-1, 16-3, 10-1, AC4 and 16-8 a stored tuber-specific cDNA library was constructed. To this end polyA RNA was isolated from potato tubers stored for 5 months at room temperature. cDNA synthesis was carried out using a cDNA synthesis kit from Pharmacia. Following adaptor ligation (EcoRI/Notl- adaptors) the cDNA was ligated into lambda ZAP II vectors following the instructions of the manufacturer (Stratagene). In vitro packaging was carried out using the Gigapack 2 II Gold packaging extract from Stratagene. 10.1.5. Isolation of cDNA clones encoding stored tuber-specific cDNA clones Following amplification of the primary cDNA library 2 x 10 5 Pfu (plaque forming units) were screened for the presence of phages hybridising to M-l-1, 16-3, 10-1, AC4 and 16-8 PCR-fragments. In all cases several independent phages hybridising to the respective PCR probes were isolated and restriction analysis following in vivo excision of the isolated clones was carried out. In four cases (Ml-1, 16-3, 10-1 and 16-8) full size cDNA clones could be obtained. After determination of the complete nucleotide sequences (Seq. 2 to 6) and Figure 19 a homology search was carried out. Based on homologies clone 16-3 corresponds to ubiquitin carboxyl-terminal hydrolase from human, Drosophila and yeast, clone 10-1 was found to be identical to the ADP-ribosylation factor 1 from potato (belonging to the family of GTP-binding proteins) and clone 16-8 has homologies to a auxin repressed protein of unknown function from strawberries. No homology was found for clone AC4. Differentially expressed clone M-l-1 encodes a protein which we have designated as MOT and which was found to have homology with bovine and human mitochondrial 2- oxoglutarate carrier protein. The sequence comparison is provided in Figure 20. 10.1.6. Nucleotide sequence of induced clones Seq. 2: 16-3 (homology to ubiquitin carboxyl-terminal hydrolase from human, Drosophila and yeast) GGGCTGCAGGAATTCGAGGCCGCTAGAGAGAGTTAAAATAGAGGAAAGGAATCCATGGCGGAAAGCACAGGCTC TAAGAAGAGATGGCTTCCTCTTGAAGCTAACCCCGATGTCATGAATCAGTTTCTTTGGGGTCTTGGTGTTCCAC CGAATGAGGCCGAGTGCTGTGATGTTTATGGGTTAGATGAAGAACTTCTGGAGATGGTGCCAAAGCCAGTGCTT GCTGTTTTATTTCTCTATCCTCTCACATCTCAGAGTGAAGAAGAGAGAATAAAGCAAGACAGCGAAACAAAGGT GCAGGATCCCAGTAGTACAGTTTACTACATGAAACAAACAGTGGGAAATGCATGCGGAACAATTGGCCTTCTTC ATGCTATTGGGAATATCACCTCTCAGATAAAACTTACCGAGGGTTCATTCTTGGACAAGTTCTTTAAATCAACC TCAAGCATGGACCCAATGCAGCGTGCTTTGTTCCTTGAAAATGATAGGGAAATGGAAGTTGCTCATTCAGTGGC AGCCACTGCTGGTGATACTGAGGCTACCGACGATGTGAACGCTCATTTCATCTGCTTCACCTGTGTTGATGGAC AACTCTATGAACTTGATGGAAGGAGGGCTGGACCTATTACACATGGCGCATCCTCTCCAAACAGCTTATTAAAG GATGCAGCCAGAGTTATCAAAAAGATAATCGAGAAAAATCCAGACTCAATCAACTTCAACGTTATTGCTATTTC CCAAAACGTTTAGGCCAATCTAGAGGCTTTTATCGATGAGATGGTTTAAACCAATTTTAGCTTTTCATGTTTCT GCCGTTTCCAGTACTATGTTTCTTCTTGTTTGCAATAAGTTACTTTTGAGAAAAAA Seq. 3: 16-8 (homology to auxin-repressed protein from strawberry) TGTTCTATCCCAGCGGACGCAGAATTTCCTTTTTTATTCTTCTCTTCTTCTCCCCTAAAACGTGAGCCGATTGG CTAACCTGCACCATGAGCTTACTTGACAAGCTCTGGGACGACACCGTTGCCGGTCCCCTGCCAGATAGTGGCCT CGGGAAACTCCGGAAGTATTCTACTTTTAGTCCGCGTTCAAATTCCGGCAAGGAATCAGAAGTTTCCACACCGA GATCCTTCACCGAGGAAGCAAGTGAGGACGTGGTGAAGGTGACGAGAAGTATCATGATAGTAAAGCCTTCCGGG AGTCAGAATAGAGATTCACCTCCAGTTTCTCCGGCCGGTACTACTCCTCCGGTATCTCCTTTTGCCGGTTCCGC TGGAAGAGAAGCATTTCGGTTCCGGCGGCGATCAGCGTCATTTGCATACGAGAATGCCAGTGGGGTTGGACCCA GAAGCCCTCGTCCTCCTTACGACCTGTGAGATATAGTCGGGTTCTCTTTTTTTGTTATCCCTCTTGAGGCGGTT GAATGTAGTATAGCTAGTCGACATACTCAACATGTTCCTGGTTGAGAGTGTTGTTTTGTGTGGTGTTTAATTTG TTTGCTTAATTTTGTAAATAGTGCAAGTGGTTCTTCATCTTGCGGATGTTGTGACGAAGGTTTAGCACAAGATG TAAGCGTCCAAGTTGGTCATGTATTCTGCTTTGTATTAAAAAAAAA Seq. 4: 10-1 (ADP-RIBOSYLATION FACTOR 1 from potato belonging to the family of GTP-binding proteins) TGGACAATAGAGATCTACTGATTTCATCCTCTCTCATCGGCCGATCTTCGATTAACGGAGATGGGGCTGTCTTT CACTAAACTCTTTAGTTCGCCTCTTTGCAAGAAAGAAATGCGAATTCTTATGGTTGGTCTCGATGCTGCTGGTA AAACCACAATTCTGTACAAGCTCAAGTTGGGAGAAATTGTTACCACTATCCCAACCATTGGTTTCAATGTGGAG ACTGTTGAATACAAAAACATCAGCTTTACTGTGTGGGATGTTGGTGGTCAGGACAAGATTAGACCTCTATGGAG GCACTATTTCCAGAACACACAGGGCCTCATCTTTGTGGTTGATAGCAATGACAGAGACCGTGTAGTTGAGGCAA GGGATGAGCTTCACAGGATGTTAAATGAGGATGAATTAAGAGAAGCTGTGTTGCTTGTTTTTGCGAACAAACAA GATCTTCCAAATGCAATGAATGCNNCTGAAATCACCGACAAGCTTGGCCTTCATTCTCTCAGACAACGACACTG GTATATCCAGAGTACATGTGCTACTTCTGGAGAAGGGCTATATGAGGGACTGGATTGGCTTTCAAACAACATCG CCAGCAAGGCCTAATGCAATGGTACTATGCTTCTTGTGTTGCTATATCCGGAGAAATAAACATCATTGTCTCGA GATTTTAAATATCTGTTCAGCTCACAATTCTGGGGAAGGCCTTACCCTTCTTCACTCTCTATGGTTTATGTCAA AGACCATGACATAGTTTACACATTGCTGGATGCACATTGGCAATGTAATGATATTTTAGTATAATATCTGGTTT TGAAACTTGGCGCAGCCGTGTGCACCATTTTGTTGTCCTGTGTGTCTGATGTTGCAATGGGTGTACAAAATGTA ATACAGATCAATAGTAAGTATCGGA Seq.5: AC4: (no homology) ACGGGACCTGGTCAATACTAATGTATCAGTCAACCAGCTCGAAAATCCACAAAATATAGAAGGGGAGGGAGGAT CACCAAGGATAAACCATCTGAACCCAGACGACAACCTCCTTCTTCTTCTTCGATCCCTTAGGGAAGAGATACCC CGATCACCTGGATTAGGAAATAAGAGGAGCAAAATAACTTCAGAAACAGGAGGAATAAAGAGATCTAGTAAGGA GAGGGGAAGCACAAACTCTGAACCTTGGAAATGTGAAGCAGAGTAATGGTCTAACAGAGTTCACCATCGACTAG TGGAAGCACAAGCATAAGAACATCCAAAGGAGAAGGAGCTTAAGTCGGTGGTTCCAGCGACATG Seq. 6: MOT Variant GAATTCGCGGCCGCAAGAGAAAGAGAGCTGAGAAAGAATGGGTGAGAAGCCAGTATCTGGAGGTGTTTGGCCTA CTGTTAAGCCATTTATTAATGGAGGTGTTTCTGGTATGCTTGCTACCTGTGTTATTCAGCCTATTGATATGATA AAGGTGAGGATACAATTGGGACAGGGATCAGCAGCTGATGTTACCAAAACCATGCTTAAAAATGAAGGCTTTGG TGCCTTTTACAAGGGTCTGTCAGCTGGGCTTCTTAGGCAGGCAACCTACACAACTGCCCGACTTGGGTCATTCA GAATTTTGACGAACAAGGCCATTGAGGCTAATGAAGGGAAGCCCTTACCTCTGTACCAAAAGGCTTTGTGTGGT CTAACTGCTGGAGCAATTGGTGCAACTGTTGGCAGTCCAGCAGATTTGGCCCTCATTCGTATGCAAGCTGATGC TACCTTGCCTTTAGCACAGAGACGCAATTACACAAATGCATTCCATGCACTCTCCCGTATTGCGGTTGATGAGG GAGTTCTAGCCCTCTGGAAAGGTGCTGGCCCAACAGTAGTAAGGGCAATGGCATTGAACATGGGTATGCTTGCC TCTTATGATCAGAGTGTGGAGTTCTTCAGGGACAACCTTGGCATGGGCGAGGCTGCTACAGTAGTAGGGGCCAG CAGTGTCTCTGGGTTCTTTGCTGCTGCTTGCAGTTTACCATTTGATTACGTCAAGACCCAGATTCAGAAAATGC AGCCAGATGCTGAAGGAAAATTGCCCTACACTGGTTCTTTCGATTGTGCCATGAAGACTTTGAAGGCAGGAGGA CCCTTCAAATTTTACACTGGATTTCCAGTATATTGTATTAGGATTGCCCCTCATGTTATGATGACTTGGATTTT CCTTAACCAAATTCAGAAGGTGGAGAAGAAAATCGGATTGTGATTGTTGCAAAAAAAGATACATCCTCTCAA GTTGAGCTTTATTAGAAATAACATCTTCGCCTTGTTGTATTAGTACTGTTTTCGCTCTTTCTTTATCCTCACGC CTTCAAAGGCTTTAAGATTTTTGTGGTGATACATTGACTCGCGGAAATTTAGGGTTAGACATTTGGTCTTTTCA ATATTCCTACCAATATAGTTTTGGGAAGATTACTTTATCCAAACTGATGGGAAGATTCTTTTAGCTGAATAATC TATGTACTTCAAAAACCGTCTTGAAGTAGGTAGTATGGAGTTCACCAATTTTGGTGTCATCTTGAACTTGATCT TGTTGCCTATTTTTGGATATACACTCATTTGTTAGCATCCTTCCTGGTATGAGCTATTGAGTATTATTGGAGTA AAAATGCATCCTAATGTTCTTGCTCCATTTGGATATATAGTTTTTTCATGCACCGCGGCCGCGAATTC VTII.Identification of promoter regions 11. Isolation of genomic clones 11.1 A genomic library oϊSolanum tuber osum var. Solar a in Zap-Express Vectors (Stratagene) (750 000 Plaques were screened) was screened. cDNA fragments from the differential display were used as probes. l l.l.l.UBL (Figure 23) Three phage were isolated in the third screen, the in vivo preparation revealed that two of them were identical and the third did not contain 5' region of the UBL gene. One of the two identical phage was used for a PCR-approach. The clone was sequenced with an oligonucleotide (GCT TTC CGC CCA TGG ATT CC) reading into the promoter. From this sequence, an additional oligonucleotide was deduced (a BamHI-site added) and used to make a PCR with the reverse-primer (Stratagene). The fragment was cloned into pGemT (Promega) and sequenced. The cloning into the pBHOl (Jefferson et al. 1987 EMBO 6) was made as BamHl fragment. Transgenic potato lines were generated containing the UBL promoter GUS construct as described previously. No detectable GUS activity was observed in a variety of tissue including stem and leaf. Tubers were harvested and a number of transgenic lines were found to exhibit GUS expression. 11.1.2.MOT (Figure 24) Six clones were isolated from the library. Two of them were be sequenced with a gene-specific primer (CCA GGA GAT GGG AAT GGA GAC CG), oligonucleotides were deduced for both clones. MOT6 and MOT3 fragments were isolated in combination with a universal Primer (Stratagene) and cloned into pGemT. MOT3 was cloned as BamHl fragment in pBI 101, MOT6 as BaniHI/Xbal fragment. 12. Construction of antisense/sense constructs 12.1.1.UBL-antisense construct A BamHl (internal restriction-site bp 301)/Asp718 (at 3 -Prime end of the cDNA in the vector pBluescript) fragment was cloned into pBinAR. pBinAR is a derivative of pB in 19, containing a 35S-Promoter (Hoefgen und WiUmitzer 1990, Plant Sci., 66,221-230). 12.1.2.MOT-antisense/sense constructs Oligonucleotides with restriction sites 5 prime BamHl base pairs 292-315 of cDNA and 3 prime Sail base pairs 993-969 were used for PCR. Th following fragments were cloned into pGemT:- BamHI/Sall-fragment in pBinAR (sense) and pBluescript (stratagene) and BamHl/ Asp718 fragment from pBluescript in pBinAR (antisense). 12.1.3.16-8 sense/antisense constructs Oligonucleotides with a restriction site 5 prime BamHl bp 6-29 cDNA and 3 prime Xbal (sense) or Asp718 (antisense) bp 682-662 cDNA were used. Fragments were cloned into pGemT, and from there into pBinAR. 12.1.4.UBL-1, MOT6 and MOT6 promoter sequences The sequences of these promoters are given in Figures 25, 26 and 27. Other modifications of the present invention will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims: CLAIMS 1. A method for the selective induction or suppression of sprouting in a plant comprising incorporating, preferably stably incorporating, into the genome of said plant by transformation a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region whereby the DNA sequence(s) in said first polynucleotide sequence is expressed during dormancy of the vegetative organ derived from said transgenic plant resulting in effective suppression of sprouting and the said suppression is neutralised by inducing expression of the DNA sequence(s) in said second polynucleotide sequence from said controllable promoter region by external application of an inducing substance such that restoration of sprouting of said vegetative storage organ is dependent on the application of the inducer. 2. A method according to claim 1 for the selective induction or suppression of sprouting in potatoes comprising incorporating, preferably stably incorporating, into the genome of a potato by transformation a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region whereby the DNA sequence(s) in said first polynucleotide sequence is expressed during dormancy of the tuber derived from said transgenic potato resulting in effective suppression of sprouting and the said suppression is neutralised by inducing expression of the DNA sequence(s) in said second polynucleotide sequence from said controllable promoter region by external application of an inducing substance such that restoration of sprouting of said tuber is dependent on the application of the inducer. 3. A method according to claim 1 or claim 2 wherein the said first polynucleotide sequence comprises a DNA sequence(s) coding for proteins involved in the mobilisation and/or utilisation of sucrose. 4. A method according to any one of the preceding claims wherein the DNA sequence(s) in said first polynucleotide sequence comprises a DNA sequence coding for an inorganic pyrophosphatase derived from plant, bacterial or fungal sources, or an invertase derived from plant, bacterial or fungal sources. 5. A method according to any one of the preceding claims wherein the DNA sequence(s) in said second polynucleotide sequence comprises a DNA sequence which is a sense, anti- sense or partial sense sequence corresponding to said first DNA sequence or DNA sequence which is capable of causing suppression of said first DNA sequence.. 6. A method according to claim 1 and claim 2 wherein the DNA sequence(s) in said first polynucleotide sequence comprises a DNA sequence which is a sense, anti-sense or partial sense sequence corresponding to a protein(s) involved in potato sprouting or DNA sequence which is capable of causing suppression of a protein(s) involved in potato sprouting. 7. A method according to any one of claims 1, 2 and 6 wherein the DNA sequence(s) in said second polynucleotide sequence comprises a DNA sequence coding for a protein involved in potato sprouting. 8. A method according to claim 1 or claim 2 wherein the DNA sequence(s) in said first polynucleotide sequence comprises a DNA sequence which is a sense, anti-sense or partial sense sequence corresponding to a protein(s) involved in mitochondrial function or DNA sequence which is capable of causing suppression of a protein(s) involved in mitochondrial function. 9. A method according to any one of claims 1 to 3 and 8 wherein the DNA sequence(s) in said second polynucleotide sequence comprises a DNA sequence coding for a protein involved in mitochondrial function. 10. A method according to claims 8 and 9 wherein said protein is MOT or ANT. 11. A method according to any one of the preceding claims wherein the tissue or organ selective promoter is the rolC promoter or a tuber promoter. 12. A method according to the preceding claims wherein the DNA sequence(s) in the second polynucleotide sequence of the construct is under the control of a controllable promoter region which may be induced chemically by the application of an external chemical stimulus. 13. A method according to claim 12 wherein the controllable promoter region is the alcPJ alcR or GST or ecdysone switch promoter. 14. A method according to any one of claims 1 to 4, 6, 8 and 10 to 13 wherein said first polynucleotide sequence comprises a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and the second polynucleotide sequence comprises a DNA sequence coding for a repressor protein capable of binding to said operator sequence. 15. A method according to claim 14 wherein said operator and repressor sequences comprise the lactose, tetracycline or lambda 434 operator/repressor sequences and mutants thereof. 16. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide sequence comprises a DNA sequence coding for a protein involved in mobilisation and/or utilisation of sucrose and said second polynucleotide sequence comprises a DNA sequence which is a sense, anti-sense or partial sense sequence corresponding to said protein or DNA sequence which is capable of causing suppression of said protein. 17. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide sequence comprises a first DNA sequence coding for a protein involved in mobilisation and/or utilisation of sucrose and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and the second polynucleotide sequence comprises a DNA sequence coding for a repressor protein capable of binding to said operator sequence. 18. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a DNA sequence(s) which is a sense, anti-sense or partial sense sequence cooesponding to a protein involved in potato sprouting or DNA sequence which is capable of causing suppression of a protein involved in potato sprouting and said second polynucleotide sequence comprises a DNA sequence(s) coding for a protein involved in potato sprouting. 19. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a first DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in potato sprouting or DNA sequence which is capable of causing suppression of a protein involved in potato sprouting and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and said second polynucleotide sequence comprises a DNA sequence(s) coding for a repressor protein capable of binding to said operator sequence. 20. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in mitochondrial function or DNA sequence which is capable of causing suppression of a protein involved in mitochondrial function and said second polynucleotide sequence comprises a DNA sequence(s) coding for a protein involved in mitochondrial function. 21. A DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and a transcription terminator region wherein said first polynucleotide comprises a first DNA sequence(s) which is a sense, anti-sense or partial sense sequence corresponding to a protein involved in mitochondrial function or DNA sequence which is capable of causing suppression of a protein involved in mitochondrial function and a further DNA sequence coding for an operator sequence operably linked to the first DNA sequence and said second polynucleotide sequence comprises a DNA sequence(s) coding for a repressor protein capable of binding to said operator sequence. 22. A DNA construct according to any one of claims 16 to 21 wherein the controllable promoter region is the alcA alcR or GST promoter region or ecdysone receptor switch. 23. A plant cell transformed with a DNA construct according to any one of claims 16 to 21 or claim 22. 24. Whole plants comprising transformed cells according to claim 23. 25. Progeny of plants according to claim 24 which progeny comprise a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region stably incorporated into their genome and the seeds or tubers of such plants and progeny. 26. A polynucleotide comprising all or part of at least one of the sequences depicted in sequence 2 , sequence 3, sequence 5 and Figure 19. 27. A polynucleotide encoding a protein having a substantially similar activity to that encoded by sequence 2, 3, 5, or Figure 19 which polynucleotide is complementary to one which to one which still hybridises with the sequence comprised by that provided in sequences 2,3 or 5 or Figure 19 when incubated at or between low and high stringency conditions. 28. A polynucleotide according to claims 26 and 27 which further comprises a promoter region operably linked thereto. 29. A polynucleotide according to any one of claims 26 to 28 which further comprises a sequence capable of targeting the translation products of the sequence to cellular or sub- cellular locations. 30. A vector comprising a polynucleotide sequence or DNA construct according to any one of the preceding claims. 31. A host cell transformed with a polynucleotide sequence according to claims 26 to 29 or a vector according to claim 30. 32. A host cell according to claim 31 which is a plant cell. 33. A whole plant derived from a cell according to claim 32 and seeds, tubers and progeny thereof. 34. The use of all or part of the DNA sequences derived from clones 16-3, 10-1, AC4, 16- 8, M-l-1 and a MOT variant having an EMBL accession number X99853 in a method according to the invention to control sprouting in plants. 35. The use of all or part of at least one of the cDNA sequences 16-3, 10-1, AC4, 16-8, M- 1-1 and a MOT variant having an EMBL accession number X99853 as gene probe(s) in the screening of genomic, cDNA and other libraries for a gene of a cooesponding genomic sequence which encodes a protein which is induced during tuber storage. 36. A DNA construct comprising a polynucleotide sequence comprising a switch promoter system operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct wherein when expression of said polynucleotide sequence is switched on from said switch promoter the resulting expression of said sense, antisense or partial sense sequence leads to down regulation of the expression of a further polynucleotide sequence encoding a transgene. 37. A method of controlling the expression of a transgene comprising transfoming a host cell with a DNA construct comprising a switch promoter system operably linked to a polynucleotide sequence comprising a sense, antisense, or partial sense transcription construct, and a further DNA construct comprising a coding sequence coding for said transgene and controlling expression of the polynucleotide sequence from said switch promoter such that the resulting expression of the said antisense, sense or partial sense construct leads to down regulation of the expression of said transgene. 38. A method according to claim 37 wherein the DNA construct comprises a GST or α/cA/ alcR switch promoter operably linked to a polynucleotide sequence comprising a sense, antisense or partial sense transcription construct . 39. A host cell transformed with a DNA construct according to claim 36. 40. A host cell according to claim 39 which is a plant cell. 41. Whole plants derived from a plant cell according to claim 40 and seeds, tubers and progeny thereof. 42. A method of identifying a site which may be a suitable target for interaction with a herbicide comprising the steps of transforming a plant with a polynucleotide sequence comprising a first DNA sequence which is capable of affecting the expression of DNA at said target site wherein expression of said first DNA sequence is under the control of a switch promoter; controlling expression of said DNA sequence from said switch promoter such that the expression of the DNA coding for the herbicide target site is down-regulated and determining the effects of said down-regulation on the plant viability. 43. A method of enhancing gene expression in tubers comprising transforming a tuber plant cell with a polynucleotide sequence comprising a DNA sequence coding for all or part of the STLS-1 leaf promoter operably linked to a further promoter region. 44. A method according to claim 43 wherein the STLS-1 leaf promoter is operably linked to the 35S CaMV promoter. 45. A method according to claim 44 wherein the STLS-1 sequence is upstream of the 35S CaMV. 46. Tubers derived from transgenic plants wherein said tubers do not sprout unless treated with a chemical inducer. 47. Tubers according to claim 46 wherein said transgenic plants have incorporated, preferably stably incorporated, into their genome a DNA construct comprising a first polynucleotide sequence comprising at least one DNA sequence operably linked to a tissue or organ selective promoter region and optionally to a transcription terminator region and a second polynucleotide sequence comprising at least one DNA sequence operably linked to and controlled by a controllable promoter region and optionally to a transcription terminator region whereby the DNA sequence(s) in said first polynucleotide sequence is expressed during dormancy of the tuber derived from said transgenic potato resulting in effective suppression of sprouting and the said suppression is neutralised by inducing expression of the DNA sequence(s) in said second polynucleotide sequence from said controllable promoter region by external application of an inducing substance such that restoration of sprouting of said tuber is dependent on the application of the inducer. 48. Potato tubers derived from transgenic plants according to claim 46 or claim 47 which do not sprout unless treated with a chemical inducer. 49. A polynucleotide comprising all or part of at least one of the sequences depicted in Figures 25, 26 or 27. 50. A polynucleotide having the same function as the sequence which is depicted in Figures 25, 26 or 27 which polynucleotide is complementary to one which still hybridises with the sequence comprised by that provided in Figures 25, 26 or 27 when incubated at or between low and high stringency conditions. 51. A polynucleotide according to claim 49 or 50 wherein the sequence is a tuber specific promoter sequence. 52. A method of controlling gene expression of a plant or a part thereof comprising transforming a plant cell with a chemically controllable plant gene expression cassette which has a first promoter operatively linked to a regulator sequence derived from the alcR gene and a controllable promoter derived from the ale A gene promoter operatively linked to a target gene, the controllable promoter being activated by the regulator protein in the presence of alcohol vapour thereby causing expression of the target gene. 53. A method, a DNA construct or a polynucleotide substantially as hereinbefore described with reference to the Figures.

Inventors: EBNETH MARCUS, JEPSON IAN, SONNEWALD UWE, EBNETH, MARCUS, JEPSON, IAN, SONNEWALD, UWE
Applicants: EBNETH MARCUS, JEPSON IAN, SONNEWALD UWE, ZENECA LTD, EBNETH, MARCUS, JEPSON, IAN, SONNEWALD, UWE, ZENECA LIMITED
Application year: 1998
Main classification: C12N15
IPC codes: C12N9, C12N15, C12Q1