Manipulating starch and storage protein biosynthesis during endosperm development to increase rice yield
2003
Sakulsingharoj, C. | Choi, S.B. | Ogawa, M. | Singh, S. | Bork, J. | Meyer, C.R. | Edwards, G.E. | Preiss, J. | Okita, T.W.
Rice yields are dependent on the quality and weight of seeds. The bulk of the seed weight is contributed by the starchy endosperm, which provides a substantial portion of food for many Asian countries. A second important but rather minor component of the starchy endosperm is protein. Despite the distinct biochemical processes, starch and storage protein syntheses display parallel responses in rice and other cereals, indicating that they are interrelated processes. The basis for this pleiotropic relationship remains unknown. In this article, we describe current findings to understand the molecular and cellular basis of starch and storage protein biosynthesis, which will provide insights into their relationship. Starch synthesis in cereal endosperm is controlled by the key regulatory enzyme ADP-glucose pyrophosphorylase (AGPase), which is present in two forms, one located in the cytoplasm and the other in the amyloplast. Using a transgenic approach, we manipulated the cytoplasmic and amyloplast AGPase enzyme activity levels during rice seed development. Based on the effects on starch biosynthesis, the cytoplasmic AGPase plays a dominant role in starch synthesis, whereas the plastid form plays only a minor role. We also describe the mechanism of storage protein synthesis in rice as a model for cereals. The results indicate the involvement of storage protein mRNA localization in protein targeting and accumulation in endosperm cells.
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