Proteomic analysis of the rice endosperm starch-deficient mutants osagps2 and osagpl2

Abstract

ADP-glucose pyrophosphorylase (AGP) catalyzes the first committed step of starch biosynthesis in higher plants. We previously isolated two rice mutants, osagps2 and osagpl2, which have starch-deficient endosperms and lack the AGP small and large subunits, respectively. In this study, we used two-dimensional gel electrophoresis and peptide mass fingerprinting to identify differentially expressed proteins in the osagps2 and osagpl2 endosperms. We found that the osagps2 and osagpl2 endosperms exhibited reduced levels of glutelins and globulins (the major seed storage proteins), protein disulfide isomerases, and the dnaK-type endoplasmic reticulum chaperone BiP. Interestingly, the osagps2 and osagpl2 endosperms had much lower levels of malate dehydrogenase and alanine aminotransferase compared with wild type endosperm, which likely function in maintaining an adequate ATP supply for starch biosynthesis in seed endosperms that are exposed to low oxygen conditions. Furthermore, metabolomics analysis showed that the levels of free amino acids and soluble sugars were significantly increased in the osagps2 and osagpl2 endosperms. These results demonstrate that carbon and nitrogen metabolisms are tightly coordinated to ensure the proper development of rice seed endosperm.