Abstract:
The invention relates to a pathogen-inducible synthetic promoter which is suitable for regulating the transcription of a nucleic acid, and includes a minimal promoter, characterized in that the minimal promoter includes a sequence motif a) dbrmwa or b) twcccmt which is disposed downstream from a TATA region and in front of a transcription starting point which is located on the minimal promoter and at which transcription of the nucleic acid to be regulated starts.

Description:
BACKGROUND OF THE INVENTION 
     Field of the invention 
     The present invention relates to a pathogen-inducible synthetic promoter which is suitable for regulating the transcription of a nucleic acid and includes a minimal promoter. Further, the present invention relates to a transgenic plant cell as well as transgenic plants. The present invention further concerns a process for producing a pathogen resistant plant. 
     Description of the Related Art   
     Various processes are known for creating plants which are resistant against pathogens such as fungi, virus, bacteria and nematodes. One of these processes employs the hypersensitive reaction (HR) of the plant, wherein the development of necrosis occurs at the location of direct contact between pathogen and plant. As a consequence of the HR a broad spectrum of pathogen defense mechanisms are triggered in adjacent cells, which prevent the further propagation of the pathogen in the plant tissue. 
     The HR can occur after expression of effector genes, such as for example avirulence genes of the pathogen and interaction with the product of a corresponding resistance gene (R-gene). The R-gene can herein already be present in the plant or, as the case may be, may be introduced by gene technology methods into the respective plant genome (Stuiver et al. 1998, Keller et al., 1999, Belbahri et al., 2001). Besides this, an over-expression or autoactivation of R-genes can lead to triggering of a HR (Tao et al., 2000, Tang et al., 1999, Bendahmane et al., 2002, Howles et al., 2005). By the over-expression of a R-gene a threshold is exceeded, which leads to initiation of a signal cascade, which conventionally is only initiated upon the presence of the pathogen or as the case may be the avirulence gene product. By triggering or activating this cascade a broad effective pathogen resistance can be achieved (Oldroyd and Staskawicz, 1998, Tang et al., 1999, Tao et al., 2000, Howles et al., 2005). Those R-genes are characterized as autoactive R-genes which are modified to the extent that for initiation of the signal cascade the presence of the pathogen/avirulence gene product is not necessary and at the same time, a reduced level of expression in comparison to the non-modified form is sufficient in order to achieve initiation of the signal cascade. 
     Stuiver et al. (1998) were able to show that the transformation of the avr9-gene from the phytopathogenic fungi  Cladosporium fulvum  under the control of the pathogen inducible Gst1-promoter from the potato in tomato plants, which carry the corresponding Cf9-gene, brought about a broad effective fungi resistance. A resistance against the oomycete  Phytophthora parasitica  var  nicotianae  could be achieved in  Nicotiana tabacum  after either the elicitor cryptogen from  P. cryptogea  or the bacterial elicitor popA from the phytopathogenic bacterium  Ralstonia solanacearum  was transformed in  N. tabacum . Both genes were under the control of the pathogen inducible promoter hsr203J from  N. tabacum  (Keller et al., 1999, Belbahri et al., 2001). 
     The system of the HR triggering requires a stringent control of the expression of the effector gene at the location of the infection. In the case of uncontrolled expression, the expression of the effector gene causes negative effects on plant growth and therewith on the harvesting of horticultural plants (Stuiver and Custers, 2001). A controlled expression can however occur by the selection of suitable pathogen inducible promoters. These should, however, no expression or only a small expression under conditions of non-infestation, however, in the case of infection, cause a significantly higher expression at the location of the infection. After transformation from two different autoactive forms of the L6 rust resistance gene from flax ( Linum usitatissimum ) in flax under the control of the natural Fis1 promoters inducible by rust from flax, two phenotypes could be observed. On the one hand, normal growth plants, which showed no improved resistance against pathogens, and on the other hand, dwarf plants, with a broad pathogen resistance (Howles et al., 2005). These results show that, depending upon the employed form of the autoactive R-gene, the result could be a promoter activity which already lies above the threshold for induction of the signal cascade, while in the phenotypically unremarkable plants the induction of the Fis1-promoters is not sufficient in order to achieve this threshold. The specificity of the natural Fis1-promoters thus is not sufficient in order to achieve the broad effective pathogen resistance without negative effects on the plant growth. 
     Natural pathogen inducible promoters frequently show a non-specific activity and are activated by numerous stimuli, so that their use for the expression of the above-described effector genes is not practical, since a HR-triggering could also occur under non-infection conditions. This “leakiness” of the promoters leads to an impairment of plant growth and thus to a reduction of the harvest yield of horticultural crops. For this reason synthetic promoters were developed, which contain the sequence motives (cis-regulatory elements) from natural, pathogen inducible promoters, which are relevant for pathogen induction. Sequence motives for other stimuli are, in contrast, removed. The cis-regulatory elements are cloned upstream of the minimal promoter, whereby a functional promoter is produced, which exhibits an elevated specificity in comparison to the natural promoters, which were isolated from the respective cis-regulatory elements (Rushton et al., 2002). As minimal promoter for dicotyledonous plants the region −46 through +8 of the 35S-gene of the Cauliflower Mosaic Virus was employed. Besides this, the use of a minimal promoter from a natural promoter, out of which the respective cis-regulatory element was cloned, are known (Perl-Treves et al., 2004). For monocotyledonous plants, the use of the minimal promoter from the Actl-gene of rice is described (Lü et al., 2000). 
     Although the described synthetic promoters are an improvement over the natural promoters, these however show background activity even under non-infection conditions. These background activities vary among individual plant types. Thus, in all plant types examined until now a pathogen inducibility could be determined, however the strength of the induction and the absolute activity of the promoters vary. In the case of a too-strong background activity in non-infected tissue, then, only a small pathogen inducibility could be determined as quotient of the promoter activity in the infected tissue divided by the promoter activity in the non-infected tissue. 
     Until now, only the employed cis-regulatory elements were considered responsible for the level of the background activity of a synthetic promoter. These have a large influence on the strength of the promoter (Rushton et al., 2002). Little investigated until now was the influence of the minimal promoter. According to the literature the minimal promoter has only a very small influence on the regulation of the promoter activity (Singh, 1998). Bhuliar et al. (2003) could however detect a clear reduction of the promoter activity of the 35S-promoter when the minimal promoter (−46 through +1) was exchanged with heterologous plant minimal promoters. These differences lead back to the different sequences of the TATA-boxes, while, according to their opinion, the flanking regions of the TATA-box of the minimal promoter are not relevant for the promoter activity. 
     It is thus the task of the present invention to provide a pathogen inducible synthetic promoter with a small background activity. 
     BRIEF SUMMARY OF THE INVENTION  
     In accordance with the invention the solution of the task is accomplished by a pathogen inducible synthetic promoter with a minimal promoter, wherein the minimal promoter includes a sequence motive
     a) dbrmwa or   b) twcccmt
 
which is situated downstream of a TATA-region and ahead of a transcription point laying on the minimal promoter at which the transcription of the nucleic acid to be regulated starts. Therein the sequence motive dbrmwa is suited primarily for dicots and the sequence motive twcccmt for monocot plants.
   

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       The invention is explained in more detail below with reference to the drawing in which: 
         FIG. 1  shows a sequence comparison between the preferred minimal promoters for dicotyledonous plants with the conserved TATA-regions and the dbrmwa-motives as well as the cleavage site Pstl and Xhol employed for cloning in the plasmid pMS231uc+; 
         FIG. 2  shows a sequence comparison between the minimal promoters, preferred for monocotyledonous plants, which are employed for the transient transformation of wheat leaves, and the sequence motive twcccmt as conserved region; 
         FIG. 3  shows an overview of the average reporter gene activity of non-infected, transgenic potato plants with a synthetic promoter comprised of the 4xGstl element and the indicated minimal promoters, cloned ahead of the luciferase gene from  Photinus pyralis  as reporter gene; 
         FIG. 4  shows a overview of the individual inductions following in vitro infection of stable, transgenic potato plants with the synthetic promoter comprised of the 4xGstl element and the indicated minimal promoters; 
         FIG. 5  shows that when transgenic sprouts were multiplied and inoculated under in vitro conditions with the zoospore suspension of  Phytophthora infestans , also with use of the cis-regulatory element 2xS/2xD a reduced background activity could be achieved with the inventive minimal promoters in comparison to 35S-minimal promoters 
         FIG. 6  shows that at the same time a stronger induction of the synthetic promoters following inoculation of the transgenic potatoes with  P. infestans  could be observed. 
         FIG. 7  shows a comparison of the normalized activity of pathogen inducible synthetic promoters comprised of an element 2xS/2xD and the minimal promoters ubil (comparison promoter), TaPAL and TaACS following biologic transformation in primary leaves of the wheat type “Taifun”. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The symbols of the sequence motive as used herein have the following meaning:
     d=nucleotide a or g or t/u   b=nucleotide c or g or t/u   r=nucleotide g or a   m=nucleotide a or c   w=nucleotide a or t/u   a=nucleotide a   t=nucleotide t   c=nucleotide c   

     In the sense of the invention a “minimal promoter” is a DNA-sequence of the promoter, which is necessary for promoter function. General transcription factors such as for example TFII-D, TFII-A, TFII-B, TFII-E and TFII-F could bond at this DNA-sequence, and form the platform for the bonding of the RNA-polymerase 11/TFII-F complex. Since the transcription of the DNA into the mRNA starts in this region, the transcription start point (TS) lies within the minimal promoter and is identified as position +1. The minimal promoter encompasses the TS and can extend for example from position −50 through position +15. Frequently a so-called TATA-box is found at the position −30, which however does not occur in all promoters. The TATA-box is a region of a sequence of thymine and adenine bases. The TATA-box is the binding location for the TATA-box binding protein (TBP). 
     Characterized as “synthetic promoters” are those promoters which do not occur in nature, are assembled from multiple elements and contain a minimal promoter as well as, upstream of the minimal promoter, at least one cis-regulatory element, which serves as the bonding location for special transcription factors. Synthetic promoters are designed according to the desired requirements and are induced or repressed by various factors. 
     “Derivatives” of a promoter are shortened or lengthened or partially identical versions of this promoter or homologs with the same, modified or singular characteristics. The expression “homology” herein means a homology of at least 70% based on DNA, which can be determined by known processes, for example, a computer supported sequence comparison (Altschul, S. F. et al., 1990). 
     The inventive pathogen inducible synthetic promoter results after transient biologic transformation in a reduced base activity in the leaf tissue of the respective plants in comparison to conventionally employed promoters with a minimal promoter such as the 35S-minimal promoter in dicotyledonous, and the corn-ubi1-minimal promoter in monocotyledonous, plants. Beyond this it was discovered that in the inventive pathogen inducible synthetic promoters the induction rate is also higher. 
     The inventive pathogen inducible synthetic promoters can thus be employed for production of transgenic plants which have a broad resistance against numerous pathogens, such as fungi, oomycetes, bacteria, virus, insects and nematodes. 
     The sequence motives dbrmwa and twcccmt lie in sense orientation on the codogenic strand between the TATA-box and the transcription start point and can also occur two or more times. Preferred sequences for minimal promoters are indicated in SEQ ID NOS: 1 through 9. 
     Cis-regulatory elements for production of pathogen inducible synthetic promoters are primarily those elements which occur in natural pathogen inducible promoters and they are responsible for pathogen induction. Their identification is described in Rushton et al. (2002). 
     Preferred cis-regulatory elements for production of synthetic promoters with use of the inventive minimal promoters are also described in WO 00/29592. From the cis-regulatory elements mentioned there, the D-box (SEQ ID NO: 10) is particularly suitable, in particular in the combination 2×S/2×D (SEQ ID NO: 11), as well as the Gst1-element, preferably in the combination 4×Gst1 (SEQ ID NO: 12). 
     Preferred cis-element combinations include in general combinations of the D-box (SEQ ID NO: 10) with the S-box or, as the case may be, the Gst1-element. Particularly preferred are, besides the above-mentioned combination 2×S/2×D (SEQ ID NO: 11), the combination 2×S/4×D (SEQ ID NO: 13); 4×S/2×D (SEQ ID NO: 14) and 2Gst1/2×D (SEQ ID NO: 15). The combination of the 2×S/4×D element (SEQ ID NO: 13) with the minimal promoter according to SEQ ID NO: 2 shows in transgenic potatoes following infection with  Phytophthora infestans  an average elevation of the reporter gene activity by a factor of 253,000 in comparison to a non-infected control. 
     If the element 4×S/2×D (SEQ ID NO: 14) was cloned ahead of the minimal promoter (SEQ ID NO: 2), an average increase in the reporter gene activity by a factor of 2,892 could be detected. With element 2×Gst1/2×D (SEQ ID NO: 15) an average increase by a factor of 2,967 in comparison to control was achieved. 
     With the inventive promoters transgenic plant cells can be produced, which can be regenerated to complete plants with improved defensive characteristics against pathogens. The inventive promoters are likewise contained in the seeds of such transgenic plants. The invention is not limited to particular types of plants. 
     The present invention is thus concerned with the process for production of a plant resistant against pathogens, in which a gene suitable for production of a pathogen resistance is introduced into a plant cell, which is under the control of a pathogen inducible synthetic promoter, and subsequently this plant cell is regenerated into a plant, characterized in that the pathogen inducible synthetic promoter is a pathogen inducible synthetic promoter as described above. 
     EXAMPLES 
       FIG. 1  shows a sequence comparison between the preferred minimal promoters (SEQ ID NOS: 1 through 7) for dicotyledonous plants with the conserved TATA-regions and the dbrmwa-motives as well as the cleavage site PstI and XhoI employed for cloning in the plasmid pMS23luc+. 
       FIG. 2  shows a sequence comparison between the minimal promoters (SEQ ID NOS: 8 and 9), preferred for monocotyledonous plants, which are employed for the transient transformation of wheat leaves. In addition to the TATA-region the sequence motive twcccmt is shown as conserved region. 
     It could be shown that the minimal promoters StGst (SEQ ID NO: 6), NtTGAA (SEQ ID NO: 5), StPSBR (SEQ ID NO: 7), NpCABE (SEQ ID NO: 2), NtRBS (SEQ ID NO: 3), NpATP2 (SEQ ID NO: 1) and Nt5EAS (SEQ ID NO: 4) exhibited a clearly reduced activity (&lt;70%) in comparison to the 35S-minimal promoter. 
       FIG. 3  shows an overview of the average reporter gene activity of non-infected, transgenic potato plants with a synthetic promoter comprised of the 4×Gst1 element (SEQ ID NO: 12) and the indicated minimal promoters, cloned ahead of the luciferase gene from  Photinus pyralis  as reporter gene (RLU=relative light unit). Stable, transgenic lines with the minimal promoters, which carry the sequence motive dbrmwa showed under controlled conditions a clearly reduced expression of the reporter gene in comparison to the 35S-minimal promoter. The smallest average activity was achieved with use of the minimal promoter of the NpATP2 gene (SEQ ID NO: 1). In these plants only 9.7% of the average activity of the 35S-minimal promoter could be measured. With use of the minimal promoters StPSBR (SEQ ID NO: 7), NtTGAA (SEQ ID NO: 5) or StGst (SEQ ID NO: 6) 18% of the activity of the 35S-minimal promoter was measured, with NtRBS-minimal promoter (SEQ ID NO: 3) 26%, with NpCABE-minimal promoter (SEQ ID NO: 2) 39% and with Nt5EAS-minimal promoter (SEQ ID NO: 4) 41%. 
     For the person of ordinary skill the manufacture of suitable constructs for transformation of plants with the inventive promoters is no problem. Thus for example the binary vectors p4×Gst1-luc-kan ( FIG. 8 ) could be produced, which was used for the stable transformation of potato plants of the variety “Baltica”. This vector is a derivative of the binary vector pGPTV (Becker et al., 1992). The binary vector p4×Gst1 luc-kan carries the luciferase gene from  Photinus pyralis  under the control of the synthetic promoter 4×Gst1:35 S minimal promoter (Rushton et al., 2002). As the termination sequence the plasmid is given the terminator of the nopalinsynthase gene from  Agrobacterium tumefaciens . The described expression cassette is localized on the T-DNA together with a functional expression cassette for the neomycinphosphotransferase gene (nptII) as selection marker. The neomycinphosphotransferase imparts to the transgenic plants resistance against kanamycin or paromycin. In order to exchange the 35S-minimal promoter with the above-described minimal promoters, the binary vector p4×Gst1 luc-kan was digested with XhoI/SalI, whereby the 35S-minimal promoter was removed, the tetramer of the Gst1-element however remained intact. The SalI cleavage location was filled with the aid of the enzyme Klenow polymerase and dNTP&#39;s in order to achieve a blunt end. The minimal promoters, cloned in the plasmid pMS23luc+, were excised using PdiI/XhoI-digestion and ligated in the binary vector and subsequently transformed in  E. coli . Binary vectors with the new sequence were transformed in the  Agrobacterium  type GV3101::pMP90 (Koncz and Schell, 1986) (An, 1987) and selected using the antibiotic kanamycin (50 mg/l). The transgenic  Agrobacterium  were employed for the transformation of potatoes of the type “Baltica” (Dietze et al., 1995). 
       FIG. 4  shows a overview of the individual inductions following in vitro infection of stable, transgenic potato plants with the synthetic promoter comprised of the 4×Gst1 element (SEQ ID NO: 12) and the indicated minimal promoters. The infection occurred in in vitro plants with a zoospore suspension of  Phytophthora infestans.    
     At various times following inoculation leaf samples of in vitro plants were removed, the sample weight was determined and 10 volumes IxCCLR buffer (Promega, Mannheim) was added. The material was homogenized with the aid of a RIA/90 Hnrnflga.ni 7 &#39;c′r OKA Labortechnik, Staufen) in buffer on ice. By centrifugation at &gt;10,000 ×g for 10 minutes the homogenate was clarified and 10 pl of the supernatant was suspended with 50 pl of the substrate LAR (Promega, Mannheim) in a luminometer tube and the light emission was determined as value for the activity of the luciferase in the luminometer (Sirius, Berthold Detection System GmbH, Pforzheim). For control or comparison in vitro plants were employed, which were raised under the same conditions and, in place of zoospores, were subject to a sham treatment with water. The average value of the quotients, in 5 independent lines, of the luciferase activity of the infected to the sham treated variants, indicates the induction of the synthetic promoter by the infection. As can be seen in  FIG. 4 , with use of the 35S-minimal promoter, a maximal induction of the luciferase activity by a factor of only 10 could be achieved 72 hours after infection. All new minimal promoters in contrast showed a clearly improved induction. The strongest induction after infection with a factor 395 was achieved 72 hours post-infection with the StPSBR minimal promoter (SEQ ID NO: 7). In general, the induction by use of the new minimal promoters could be improved at time 72 hours post-induction by a factor of 3.5 with StGst minimal promoter (SEQ ID NO: 6) to a factor of 39.5 with StPSBR minimal promoter (SEQ ID NO: 7) in comparison to 35S-minimal promoter. Interestingly, clear differences in the kinetics of the induction following pathogen induction exist between the minimal promoters. While the most discernible induction is measurable with use of the 35S-minmal promoter 72 hours post induction, this also applies with use of the StPSBR, NtTGAA, StGst, NtRBS as well as NpATP2 minimal promoter. For NpCABE and Nt5EAS promoters in comparison a strong activation is already detectable at time interval 9 and the induction remains at approximately the achieved level over the remaining test period. 
     The preferability of the new minimal promoters was shown following fusion with the cis-element combination 2×S/2×D. For this, potato plants were stably transformed with the binary vectors p2×S/2×Dluc-kan, p2×S/2×DNpCABEiuc-kan and p2×S/2×DNtTGAAluc-kan. The binary vectors were produced in that the 4×Gst1-element from the above-described binary vector with the new minimal promoter and the 4×Gst1-element were eliminated via Bcul/Eco1471-digestion and the element 2×S/2×D (SEQ ID NO: 11) was introduced as Bcul/Eco321-fragment. Binary vectors with the new sequence were transformed in the  Agrobacterium  type GV3101::pMP90 (Koncz and Schell, 1986) (An, 1987) and selected using the antibiotic kanamycin (50 mg/l). The transgenic  Agrobacterium  were employed for the transformation of potato of the type “Baltica” (Dietze et al., 1995). Transgenic sprouts were multiplied and inoculated under in vitro conditions with the zoospore suspension (50,000 spores/ml) of  Phytophthora infestans . It could be shown, that also with use of the cis-regulatory element 2×S/2×D (SEQ ID NO: 11) a reduced background activity could be achieved with the inventive minimal promoters in comparison to 35S-minimal promoters ( FIG. 5 ). At the same time a stronger induction of the synthetic promoters following inoculation of the transgenic potatoes with  P. infestans  could be observed ( FIG. 6 ). The amplification of the induction was not so pronounced at the later time (3 days post infection=3 dpi) as could be observed following use of the 4×Gst1-element. Two days following infection however by the use of the new minimal promoter a clearly stronger induction following pathogen attack could be observed. Herewith the use of these minimal promoters has as a consequence an improvement of the kinetics of the synthetic promoter, so that the reaction to pathogen attack occurs earlier, in comparison to the synthetic promoter using the 35S-minimal promoter. 
       FIG. 7  shows a comparison of the normalized activity of pathogen inducible synthetic promoters comprised of an element 2×S/2×D (SEQ ID NO: 11) and the minimal promoters ubi1 (comparison promoter), TaPAL (SEQ ID NO: 9) and TaACS (SEQ ID NO: 8) following biologic transformation in primary leaves of the wheat type “Taifun”. As can be seen, the new minimal promoters TaPAL and TaACS in wheat have a reduced base activity in comparison to ubi1-minimal promoter. While a normalized activity of 0.17 was measured with the ubi1-minimal promoter, with use of the TaPAL-minimal promoter this could be reduced to 0.072, and with use of the TaACS-minimal promoter it could be reduced to 0.13. 
       FIG. 9  shows the plasmid pubiTATARucII, which contains the cDNA with the luciferase gene from  Renilla reniformis , as it exists in the commercially available plasmid pRL-Null. The cDNA is under the control of the ubi1-minimal promoter. The ubi1-minimal promoter includes the sequence range from −45 through +76 relative to the transcription start point. For elevating the expression strength the first intron of the ubi1-gene is maintained in its natural context in the plasmid ahead of the reporter gene. The plasmid serves for cloning the cis-regulatory element 2×S/2×D (SEQ ID NO: 11), in order thereby to produce a pathogen inducible synthetic promoter. The ubi1-minimal promoter was exchanged for the new minimal promoter for improving the characteristics of the synthetic promoter. 
     REFERENCES 
     An, G. (1987). Binary Ti vectors for plant transformation and promoter analysis. Methods Enzymol. 153: 292-305 
     Altschul, S. F. et al. (1990), Basic Local Alignment search tool, J. Mol. Biol. 215: 403-410 
     Becker, D. et al. (1992). New plant binary vectors with selectable markers located proximal to the left T-DNA border. Plant Mol Biol. 29: 1195-1 197 
     Belbahri, L. et al. (2001). A local accumulation of the  Ralstonia solanacearum  PopA protein in transgenic tobacco renders a compatible plant-pathogen interaction incompatible. Plant J. 28: 419-430 
     Bendahmane, A. et al. (2002). Constitutive gain-of-function mutants in a nucleotide binding site-leucine rich repeat protein encoded at the Rx locus of potato. Plant J. 32: 192-204 
     Bhullar, S. (2003). Strategies for the development of functionally equivalent Promoters with minimum sequence homology for transgenic expression in plants: cis-elements in a novel DNA context versus domain swapping. Plant Physiol. 132: 988-998 
     Dietze, J. et al. (1995).  Agrobacterium -mediated transformation of potato ( Solanum tuberosum ). In: Gene Transfer to Plants XXII (Potrykus, I. and Spangenberg, G., eds.). Berlin: Springer Verlag, pp 24-29 
     Howles, P. et al. (2005). Autoactive alleles of the flax L6 rust resistance gene induce non-race-specific rust resistance associated with the hypersensitive response. Mol. Plant-Microbe Interact. 18: 570-582 
     Keller, H. et al. (1999). Pathogen-induced elicitin production in transgenic tobacco generates a hypersensitive response and non-specific disease resistance. Plant Cell11. 223-235 
     Koncz, C. and Schell, J. (1986). The promoter of TL-DNA gene 5 controls the tissue specific expression of chimeric genes carried by a novel type of  Agrobacterium  vector. Mol. Gen. Genet., 204: 383-396 
     Lü, H. et al. (2000). Construction of chimeric inducible Promoters by elicitors of rice fungal blast pathogen and their expression in transgenic rice. Chinese Science Bulletin 45: 242-246 
     Oldroyd, G. E. D. and Staskawicz, B J. (1998). Genetically engineered broad spectrum disease resistance in tomato. Proc. Natl. Acad. Sei. U.S.A. 95: 10300-10350 
     Maas, C. et al. (1991). The combination of a novel stimulatory element in the first exon of the maize Shrunken-1 gene with the following introni enhances reporter gene expression up to 1000-fold. Plant Mol Biol. 16: 199-207 
     Perl-Treves, R. et al. (2004). Early induction of the  Arabidopsis  GSTF8 Promoter by specific strains of the fungal pathogen  Rhizactonia solani . Mol. Plant-Microbe Interact. 17: 70-80 
     Rushton, P J. et al. (2002). Synthetic plant promoters containing defined regulatory elements provide novel insights into pathogen- and wound-induced signaling. Plant Cell 14, 749-762 
     Singh, K. B. (1998). Transcriptional regulation in plants: the importance of combinatorial control. Plant Physiol. 118: 11 11-1 120 Stuiver, M. H. and Güsters, J. H. H. V. (2001). Engineering disease resistance in plants. Nature 4 11: 865-868 
     Stuiver, M. H. et al. (1998). Infection-induced expression of the avirulence gene avr9 in transgenic Cf9 tomato plants confers resistance to fungal pathogen attack. 7 th  International congress of plant pathology, 9-16 Aug., Edinburgh, Scotland 
     Tang, X. et al. (1999). Overexpression of Pto activates defense responses and confers broad resistance. Plant Cell 11:15-29 
     Tao, Y. et al. (2000). Mutational analysis of the  Arabidopsis  nucleotide binding site-leucine-rich repeat resistance gene RPS2. Plant Cell 12: 2541-2554