Os08g0191433

Annotated Information

Figure A. SEM observations of a cross section of rice seeds were conducted

Function

OsSSIIIa plays an important role in starch granule structures, amylose ratios and metabolite changes of starch grains in the monocot plant rice. This gene OsIIIa is are major enzymes involved in starch biosynthesis in developing rice (Oryza sativaL.) endosperm.If OsSSIIIa gene encoding deletion or mutation , this will lead to changes in the grain starch -related traits.. It is also likely to be a good subject for exploring the link between cell growth and cell wall formation in rice.

Mutation

Figure B. Phylogenetic relationships and genomic structures of rice starch synthase genes.

• FigureB shows the reduction of SSIIIa activity affects the distinct granular structure of starch in the endosperm. In the wild type, the

endospermstarch granules formed similarly sized polygonal granules with sharp edges. Several starch granules were tightly packed into the myloplasts, which were very abundant in the endosperm cells. In contrast, the amyloplasts of SSIIIa mutants were round shaped and relatively loosely packed into endosperm cell.

• Starch synthase IIIa (SSIIIa)-deficient rice (Oryza sativa) mutants were generated using retrotransposon insertion and chemicalmutagenesis. The lowest migrating SS activity bands on glycogen-containing native polyacrylamide gel, which were identifiedto be those for SSIIIa, were completely absent in these mutants, indicating that they are SSIIIa null mutants. The amylopectin B2 to B4chains with degree of polymerization (DP) $ 30 and the Mr of amylopectin in the mutant were reduced to about 60% and 70%of the wild-type values, respectively, suggesting that SSIIIa plays an important part in the elongation of amylopectin B2 to B4chains. Chains with DP 6 to 9 and DP 16 to 19 decreased while chains with DP 10 to 15 and DP 20 to 25 increased in the mutantsamylopectin. These changes in the SSIIIa mutants are almost opposite images of those of SSI-deficient rice mutant and werecaused by 1.3- to 1.7-fold increase of the amount of SSI in the mutants endosperm. Furthermore, the amylose content and theextralong chains (DP $ 500) of amylopectin were increased by 1.3- and 12-fold, respectively. These changes in the compositionin the mutants starch were caused by 1.4- to 1.7-fold increase in amounts of granules-bound starch synthase (GBSSI). The starchgranules of the mutants were smaller with round shape, and were less crystalline. Thus, deficiency in SSIIIa, the second majorSS isozyme in developing rice endosperm affected the structure of amylopectin, amylase content, and physicochemicalproperties of starch granules in two ways: directly by the SSIIIa deficiency itself and indirectly by the enhancement of both SSIand GBSSI gene transcripts..
  
  

Structured Information

Category:Genes]]

References

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Naoko Fujita;Mayumi Yoshida;Tomonori Kondo;Kaori Saito;Yoshinori Utsumi;Takashi Tokunaga;Aiko Nishi;Hikaru Satoh;Jin-Hee Park;Jay-Lin Jane;Akio Miyao;Hirohiko Hirochika and Yasunori Nakamura. Characterization of SSIIIa-Deficient Mutants of Rice: The Function of SSIIIa and Pleiotropic Effects by SSIIIa Deficiency in the Rice Endosperm. Plant Physiology, 2007, 144(4): 2009-2023.