Use of cyanobacterial fructose-1,6-bisphosphatase to improve growth of plants

Abstract: Using the technique of recombinant DNA, the photosynthetic ability, in other words the primary metabolism of a higher plant, was improved to enhance the growth. This improvement results in increase of harvest potentiality and earlier harvest of crops. A cyanobacterial fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase is phenotypically expressed in chloroplasts of a higher plant to improve the productivity of the higher plant.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to a method for enhancing the photosynthetic activity and growth of a higher plant to increase its harvest yield and/or to enable its earlier harvest. 2. Description of related art The development of a recombinant DNA technique has realized the incorporation of a certai exogenous gene into a higher plant in expression regulation of an existing gene therein. DE 19 502 053 discloses the expression of a deregulated or unregulated bacterial fructose-1,6-bisphosphatase (FBPase) in the cytosol of plants to improve plant yield. Raines Christine A et al. in "Journal of Experimental Botany", Oxford University press, GB, vol. 50, no. 330, January 1999, pages 1-8, refer to the characterization of sedoheptulose-1,7-bisphosphatase (SBPase) and its importance in photosynthesis. It is shown that transgenic plants with anti-sense constructs had reduced levels of a certain enzyme resulting in photosynthetic activity and reduced growth rates. It is envisaged that plants with increased levels of SBPase could support higher rates of photosynthesis. Tamoi Masahiro et al. describe in "Archives of Biochemistry and Biophysics", vol. 334, no. 1, 1996, pages 27-36 the isolation and characterization of the FBPase/SBPase from Synechococcus PPC 7942 which is identical with the enzyme used in the present application. The problem of the present invention relates to the provision of higher plants having an enhanced photosynthesis rate and improved growth. SUMMARY OF THE INVENTION Despite of it, no attempts have been performed on phenotypic expression of a certain gene in a higher plant using recombinant DNA technique to enhance the photosynthesis, which is a primary metabolism of a higher plant, and to improve its growth. The object of this invention is to achieve phenotypic expression of a certain gene in a higher plant using recombinant DNA technique to enhance the photosynthesis, which is primary metabolism of a higher plant, to improve the crop productivity and yield potentiality and/or to enable the earlier harvest of the crop. This invention provides a method for improving the productivity of a higher plant having chloroplasts by the phenotypic expression of cyanobacterial fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase in the chloroplasts. Moreover, this invention provides a transgenic plant comprising a higher plant with a DNA fragment incorporated therein, the DNA fragment containing a base sequence coding cyanobacterial fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase. The fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase (SBPase) in the chloroplasts of a higher plant are the key (rate determining) enzymes of a photosynthetic reductive carbon system. The activities of these enzymes are regulated by photoreduction-potentiality. On the other hand, fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase (FBPase/SBPase), derived from cyanobacterium Synechococcus PCC 7942 gene, is found widely in a specific type of an prokaryotic alga a cyanobacterium. The primary structure and enzyme properties of cyanobacterial FBPase/SBPase are different from those of the FBPase or SBPase found in the chloroplasts of a higher plant. In addition, cyanobacterial FBPase/SBPase is composed of one protein, that is, a bifunctional enzyme exhibiting two kinds of enzyme activities, FBPase and SBPase. FBPase-I, derived from cyanobacterium Synechococcus PCC 7942 gene, is a tetramer consisting of four subunits of 40kDa identical with each other. After the treatment by 1 mM H 2 O 2 , the purified enzyme retained more than 80% of native enzyme activity. The enzyme activity of FBPase-I was inhibited by AMP (K i =0.26mM), which is a specific inhibitor of cytoplasm-type FBPase. However, it was not inhibited by fructose-2,6-P 2 . The optimum pH for the enzyme activity was 8.0 and pI value of the enzyme was 4.8. FBPase-I hydrolyzed not only fructose-1,6-bisphosphate (Fru1,6-P 2 ), but also sedohepculose-1,7-bisphasphate (Sed1,7-P 2 ). The activities of the purified enzyme for Fru1,6-P 2 and Sed1,7-P 2 were 11.7 µmol/min/mg protein and 12.1 µmol/min/mg protein, respectively. The Km values for Fru1,6-P 2 and Sed1,7-P 2 were 52 µM and 118 µM, respectively. The enzyme activity was proved to be dependent on Mg 2+ concentration, also equally to typical FBPase. The dose-response curve showed sigmoidal curve equally to plastid FBPase, and the S 0.5 value was shown to be 1.4 ± 0.1 mM. This enzyme itself was described in "Archives of Biochemistry and Biophysics, Vol. 334, No. 1, pp. 27 to 36, 1996 : Molecular characterization and resistance to hydrogen peroxide of two fructose-1,6-biphosphatase from Synechococcus PCC 7942". The inventor incorporated fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase, isolated from the cyanobacterium Synechococcus PCC 7942, into a tabacco plant so that the expressed protein was transferred to its chloroplasts. The FBPase activity, the SBPase activity and the photosynthetic ability of the transgenic plant were compared to those of the wild type strain. The results measured 7 weeks after seeding showed significant increase of these activities in the transgenic plant. Furthermore, after certain period of cultivation, the plant bodies of the transgenic plant proved to be taller than those of the wild type strain. In the transgenic plant, the areas of the blades, the diameters of the stalks, and the numbers and lengths of the roots were larger than those in the wild type strain. In addition, the contents of hexose, sucrose and starch were proved to be increased in blades, stalks and roots of the transgenic plant, compared with those of the wild type strain. Accordingly, the photosynthetic ability of the transgenic plant, obtained by incorporation of cyanobacterial FBPase/SBPase into a tabacco plant, was improved. As the result, the ability of the transgenic plant to synthesize carbohydrate and starch is increased, and the growth was enhanced, indicating the increase of final anabolism of the transgenic plant. Therefore, incorporation of cyanobacterial FBPase/SBPase into the chloroplasts of a higher plant was proved to be a very effective technique for producing high-yield plants. The effect might be explained as follows. Triggered by environmental stresses, light and oxygen toxicity causes various kinds of injuries to plant bodies, resulting in a critical and limiting factor of food production. Contrary to FBPase and SBPase derived from a higher plant, cyanobacterial FBPase/SBPase is resistant against oxygen injury and thus considered to function under various environmental stresses. Moreover, a gene encoding the cyanobacterial FBPase/SBPase does not exist in higher plants, thereby eliminating the possibility of adverse effects by gene silencing, In this invention, a vector to produce a recombinant DNA includes plasmids pBI101, pIN19 and pMSH-1. A wide variety of useful cultivated plants and woods capable of photosynthesis can be adopted as a higher plant in which the inventive recombinant DNA is incorporated. For example, the invention may be applied to serials such as maize, rice, wheat, barely, oat wheat, millet and barnyard millet, beans such as soy bean, vegetables such as potato and tomato, useful cultivated plants such as coleseed, cotton and tabacco, and trees. An amino acid sequence may be deleted from or added to the amino acid sequence of sequence number 1, or a part of the sequence of the sequence number 1 may be substituted with another amino acid sequence in the scope of this invention, so far as the resulting peptide retains its enzymatic activity properties as fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphasphatase. Preferably, not lower than 85 percent, more preferably not lower than 95 percent of the amino acid sequence may be overlapped or identical with the amino acid sequence of the sequence number 1. In a base sequence of sequence number 2, a base sequence referred to as base numbers from 1 to 1068 is essential for this invention, because this base sequence corresponds to a structural gene portion, that is, an amino acid sequence of the sequence number 1. In addition, a base sequence referred to as base numbers from -180 to 1170 is the most preferred embodiment of this invention. These and other features and advantages of this invention will become apparent upon a reading of the detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the structure of a plasmid incorporated into tabacco chloroplasts. Fig. 2 is a graph showing the heights of the plant bodies of a wild type strain and a transgenic plant under water culture. Fig. 3 is a graph showing the photosynthetic ability of a wild type strain and a transgenic plant. Fig. 4 is a photograph showing appearance of plant bodies of a wild type strain and a transgenic plant, on the 112th day of cultivation under water culture, Fig. 5 is a photograph showing the appearance of blades and stems of a wild type strain and a transgenic plant, on the 112th day of cultivation under water culture, Fig. 6 is a photograph showing the appearance of roots of a wild type strain and a transgenic plant, on the 112th day of cultivation under water culture. Fig. 7 is a graph showing contents of intermediate metabolites of a wild type strain and a transgenic plant. DETAILED DESCRIPTION OF EMBODIMENTS As shown in Fig. 1, tomato rbcS promoter, coding region of a transit peptide and cyanobacterial fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase (S.7942 FBP/SBPase) gene (fbp-I) were conjugated with pBI101 to construct a plasmid. The gene named fbp-I indicates a base sequence referred to as base numbers from -180 to 1170 of the sequence number 2, derived from cyanobacterial Synechococcus PCC7942. The plasmid was incorporated into Agrobacterium tumefacience LBA4404, which was used for infection of leaf disk of tabacco (Nicotiana tabacum cv Xanthi), to incorporate fbp-I into a tabacco nuclear gene. After isolating the genomic DNA, incorporation of fbp-I was confirmed by PCR and immunoblotting methods. 7 strains of transformants (TFI-1 to TF1-7) were obtained. The chloroplasts was isolated from transformed strains (T2 generation), then expression of S.7942 FBPase/SBPase was confirmed by Western blotting. Moreover, it was confirmed, by cell fractionation, that the protein expressed from the incorporated gene is localized in the chloroplasts. (The FBPase activity, SBPase activity and photosynthetic activity) The FBPase activity of the blades of the plant body of the transgenic tabacco cultivated 7 weeks after seeding was compared with that of the wild type strain without the incorporated gene. The result showed that the enzyme activity of the wild type strain was 1.04±0.22 µmol/min/mg chlorophyll and that of the transgenic plant was 1.82±0.24 µmol/min/mg chlorophyll. Therefore, the activity of the transgenic plant is 1.75 times higher than that of the wild type strain. The SBPase activity was also compared. The SBPase activity of the wild type strain was 1.37 µmol/min/mg chlorophyll and that of the transgenic plant was 2.40 µmol/min/mg chlorophyll. Therefore, the activity of the transgenic plant is 1.75 times higher than that of the wild type strain. The photosynthetic activity under conventional condition (360 ppm CO 2 ) was compared. As the result, significant difference between the wild type strain and the transgenic plant was not observed under illumination of 0, 10, 50 and 100 µE/s/m 2 . However, the photosynthetic activity of the transgenic plant increased significantly, under illumination of 200 µE/s/m 2 , compared with that of the wild type strain. Under 1600 µE/s/m 2 of illumination, the enzyme activity of the wild type strain was 1.24 times higher than that of the wild type strain. These results are shown in Fig. 3. (Effect of transformation upon the plant growth) Using Hogrant medium, water culture was performed on the wild type strain and the transgenic plant. The experiment was performed under condition of 400 µmol/m 2 /s, a relative humidity of 60% and a temperature of 25°C. On the 63rd day, 72nd day, 77th day, 82nd day, 85th day, 90th day, 97th day, 102nd day, 105th day, 109th day, 112th day of cultivation, the heights of the plant bodies were measured. The results are shown in Fig. 2. On the 64th day of cultivation, the height of the wild type strain was 14.0±4.6cm and that of the transgenic plant was 16.6±2.9cm. However, on the 112th day of cultivation, the height of the wild type strain was 58.3±7.0cm and that of the transgenic plant was 84.5±7.8cm, indicating significant enhancement of growth in the transgenic plants (about 1.45 times). The pictures in Fig. 4 show plant body of the wild type strain (left) and that of the transgenic plant (right). During the whole period of growth, the blades, stems and roots of the transgenic plant grew better than those of the wild type strain. That is, the leaves are thicker with broader surface area, the stems are thicker and the number of roots are larger with each root longer. Fig. 5 is a photograph showing the appearance of the blades and stems on the 112th day of cultivation, and the wild type strain is shown in the left and the transgenic plant is shown in the right. Fig. 6 is a photograph showing the appearance of roots on the 112th day of cultivation, and the wild type strain is shown in the left and the transgenic plant is shown in the right. (The contents of metabolic intermediates) The contents of metabolic intermediates (hexose, sucrose, starch) were measured on upper blades (fourth blade from the top), lower blades (third blade from the bottom), stems and roots of plant bodies 12th week after seeding, for comparing the contents between the wild type strain and the transgenic plant. The results are shown in Fig. 7. The contents of metabolic intermediates in the transgenic plant increased significantly in all parts, including the upper blades, the lower blades, the stems and the roots, compared with the wild type strain. Especially, hexose and sucrose contents in the upper blades considerably increased. The accumulation of starch was observed in the lower blades. This is considered that sucrose synthesized in the upper blades was transferred into the lower blades. As shown in these results, photosynthesis in higher plants was enhanced by this invention, increasing the production of carbohydrate and starch bio-synthesized in the transgenic plant to promote the plant growth. The dry weight of the plant bodies of the wild type strain was 14.1±2.2g at the period of flower bud production, and that of the transgenic plant was 21.0±1.9g. The dry weight of the transgenic plant increased 1.5 times compared with that of the wild type strain, indicating increase of final anabolism. As described above, photosynthetic ability was enhanced in the transgenic plant of this invention compared with the wild type strain to improve the capability of biosynthesis of carbohydrate and starch, to promote the growth and to increase the final anabolism in the transgenic plant. Accordingly, the incorporation of FBPase/SBPase into chloroplasts of a higher plant is proved to be a very effective technique to produce a high-yield crop. There has been no technique which enables production of a high-yield crop using recombinant DNA technique to improve the photosynthetic ability of a higher plant, which is its primary metabolism. Therefore, this invention provides an important key technique to solve the coming crisis of food shortage. SEQUENCE LISTING <110> NARA INSTITUTE OF SCIENCE AND TECHNOLOGY <120> A METHOD FOR IMPROVING PRODUCTIVITY OF HIGHER PLANTS <130> EP 99 125 331.1 <140> EP 99125331.1 <141> 1999-12-20 <150> JP 11-62,891 <151> 1999-03-10 <160> 3 <170> PatentIn Ver. 2.1 <210> 1 <211> 356 <212> PRT <213> Cyanobacterium Synechococcus <220> <221> CHAIN <222> (1)..(356) <223> aa seq. of one subunit of fructose-1,6-bisphosphatase/sedoheptulose-1,7-bis-phosphatase (tetrameric enzyme composed of 4 identical subunits) derived from the Cyanobacterium Synechococcus PPC 7942 gene <400> 1 <220> 2 <211> 1350 <212> DNA <213> Cyanobacterium Synechococcus <220> <221> gene <222> (1)..(1350) <223> gene encoding fructose-1,6-bisphosphatase/sedoheptulose-1,7-bis-phosphatase derived from Cyanobacterium Synechococcus PPC 7942 <220> <221> 5'UTR <222> (1)..(180) <220> <221> CDS <222> (181)..(1248) <220> <221> misc_feature <222> (181) .. (183) <223> amino acid encoded by this codon differs from the amino acid given in the respective position in SEQ ID NO. 1 <400> 2 <210> 3 <211> 356 <212> PRT <213> Cyanobacterium Synechococcus <400> 3

Claims: A method for improving the productivity of a higher plant having chloroplasts by phenotypically expressing fructose-1,6-bisphosphatase/ sedoheptulose-1,7-bisphosphatase derived from Cyanobacterium Synechococcus in said chloroplasts. A method for improving the productivity of a higher plant having chloroplasts by phenotypically expressing a protein containing the following amino acid sequence (a) or (b) in said chloroplasts: (a) an amino acid sequence as depicted in SEQ ID No. 1, (b) an amino acid sequence in which a part of said amino acid sequence (a) is deleted or another amino acid sequence is added to said amino acid sequence (a) or a part of said amino acid sequence (a) is substituted with another amino acid sequence, the amino acid sequence (b) exhibiting enzyme activity as fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase. A transgenic higher plant having chloroplasts, the transgenic plant comprising a DNA fragment incorporated in said higher plant, and the DNA fragment containing a base sequence coding fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase derived from Cyanobacterium Synechococcus. The transgenic plant according to claim 3, wherein phenotypic expression of fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase is localized in said chloroplasts. A transgenic higher plant having chloroplasts, the transgenic plant comprising a DNA fragment incorporated in said higher plant, and the DNA fragment containing a base sequence coding the following amino acid sequence (a) or (b): (a) an amino acid sequence as depicted in SEQ ID No. 1, (b) an amino acid sequence in which a part of said amino acid sequence (a) is deleted or another amino acid sequence is added to said amino acid sequence (a) or a part of said amino acid sequence (a) is substituted with another amino acid sequence, the amino acid sequence (b) exhibiting enzyme activity as fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase. The transgenic plant according to claim 5 wherein said DNA fragment contains the following base sequence (c) or (d): (c) a base sequence referred to as base numbers from 1 to 1068 as depicted in SEQ ID No. 2, (d) a base sequence which hybridizes with said base sequence (c) under stringent condition, the base sequence (d) encoding a protein exhibiting enzyme activity as fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase. The transgenic plant according to claim 6, wherein said DNA fragment contains the following base sequence (e) or (f): (e) a base sequence referred to as base numbers from -180 to 1170 as depicted in SEQ ID No. 2, (f) a base sequence which hybridizes with said base sequence (e) under stringent condition, the base sequence (f) encoding a protein exhibiting enzyme activity as fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase. The transgenic plant according to claim 5, wherein the phenotypic expression relating to said DNA fragment is localized in said chloroplasts. The transgenic plant according to claim 6 or 7, wherein the phenotypic expression relating to said DNA fragment is localized in said chloroplasts.

Inventors: SHIGEOKA SHIGERU, YOKOTA AKIHO, SHIGEOKA, SHIGERU, YOKOTA, AKIHO
Applicants: NARA INST OF SCIENCE AND TECHN, NARA INSTITUTE OF SCIENCE AND TECHNOLOGY
Application year: 1999
Main classification: C12N9
IPC codes: C12N5, C12N15, A01H1, C12N9