Plant molecular breeding with the modified metabolic capacity of transitory starch for increase of biomass resources

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Plants have the ability to convert light energy to chemical energy and to fix atmospheric carbon dioxide by using the chemical energy. It is very important in the survival of plants to utilize the photoassimilate efficiently. It is generally known that the photosynthetic capacity is positively correlated with the accumulation of transitory starch. Therefore, to reinforce the metabolic capacity of transitory starch is expected to lead elevation of the photosynthetic capacity, the growth and the productivity. We have employed the modification of allosteric properties of ADP-glucose pyrophosphorylase (AGPase), which is the key enzyme of plant starch biosynthesis. Arabidopsis plants with modified allosteric AGPase showed the increase of metabolic capacity of transitory starch and thereby the plant growth. The aim in this study was to obtain the basic data for the improvement of rice plant productivity.1.Expression of AGPase that is insensitive to known allosteric moleculesAGPase from Bacillus stearothermophillus is insensitive to known allosteric molecules. In this study, the gene for B.stearothermophillus AGPase (BsAGP) was introduced into Arabidopsis plants that is deficient in the leaf AGPase isoform. The AGPase activity and transitory starch levels in transgenic plants recovered only to the same levels as wild-type plants, indicating that BsAGP is regulated by unknown molecules in plants.2.Organ-specific expression profiles of the genes for rice AGPase subunitsAnalysis of RT-PCR products showed that 6 rice AGPase genes expressed differently in several organs. One of the 6 genes generated two transcripts by alteenative splicing, whose proteins located in different subcellular compartments, cytosol and amyloplasts.3.Expression pattern of the candidate gene for rice ADP-glucose transporterAnalysis of RT-PCR products indicated that the transcripts for the candidate of rice ADP-glucose transporter accumulates predominantly in endosperms.