Os06g0160700

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Annotated Information

Function

Please input function information here. Four starch synthase I (SSI)-deficient rice (Oryza sativa) mutant lines were generated using retrotransposon Tos17 insertion. The mutants exhibited different levels of SSI activities and produced significantly lower amounts of SSI protein ranging from 0% to 20% of the wild type. The mutant endosperm amylopectin showed a decrease in chains with degree of polymerization (DP) 8 to 12 and an increase in chains with DP 6 to 7 and DP 16 to 19. The degree of change in amylopectin chain-length distribution was positively correlated with the extent of decrease in SSI activity in the mutants. The structural changes in the amylopectin increased the gelatinization temperature of endosperm starch. Chain-length analysis of amylopectin in the SSI band excised from native-polyacrylamide gel electrophoresis/SS activity staining gel showed that SSI preferentially synthesized DP 7 to 11 chains by elongating DP 4 to 7 short chains of glycogen or amylopectin. These results show that SSI distinctly generates DP 8 to 12 chains from short DP 6 to 7 chains emerging from the branch point in the A or B1 chain of amylopectin. SSI seemingly functions from the very early through the late stage of endosperm development. Yet, the complete absence of SSI, despite being a major SS isozyme in the developing endosperm, had no effect on the size and shape of seeds and starch granules and the crystallinity of endosperm starch, suggesting that other SS enzymes are probably capable of partly compensating SSI function. In summary, this study strongly suggested that amylopectin chains are synthesized by the coordinated actions of SSI, SSIIa, and SSIIIa isoforms.

Expression

Please input expression information here. In rice, there are 10 SS isoforms separated into five types; two granule-bound starch synthase (GBSS) isoforms (GBSSI and GBSSII) in the GBSS type, one SSI isoform in the SSI type, three SSII isoforms (SSIIa [SSII-3], SSIIb [SSII-2], and SSIIc [SSII-1]) in the SSII type, two SSIII isoforms (SSIIIa [SSIII-2] and SSIIIb [SSIII-1]) in the SSIII type, and two SSIV isoforms (SSIVa [SSIV-1] and SSIVb [SSIV-2]) in the SSIV type. Soluble fraction from rice developing endosperm was separated by anion-exchange chromatography with a linear gradient of 0 to 0.5 M NaCl. One peak of SS activity that eluted at 0.2 to 0.25 M of NaCl was detected in the presence of 0.5 M citrate and the absence of exogenous primers, whereas two SS activity peaks were detected at about 0.2 to 0.25 M and 0.35 M, in the absence of citrate but in the presence of glycogen primer. As in maize, SSI in rice exhibited SS activity even in the absence of exogenous primers, while rice SSIIIa activity was dependent on the exogenous primer (Fig. 1A). Native-PAGE/SS activity staining of each fraction from the HitrapQ column in gel containing rice amylopectin indicated that the strong activity middle band found in fraction numbers 3 to 5 corresponds to SSI activity. Extensive searches for starch synthase genes were done in the databases of both the whole genome and full-length cDNAs of rice, and ten genes were revealed to comprise the starch synthase gene family. Multi-sequence alignment analysis of the starch synthase proteins from rice and other plant species suggested that they were grouped into five classes, soluble starch synthase I (SSI), SSII, SSIII, SSIV and granule-bound starch synthase (GBSS). In rice, there was one gene for SSI, three for SSII and two each for SSIII, IV and GBSS. The expression pattern of the ten genes in the developing caryopsis was examined by semiquantitative RT–PCR analysis. Based on the temporal expression patterns, the ten genes could be divided into three groups: (i) early expressers (SSII-2, III-1, GBSSII), which are expressed in the early stage of grain filling; (ii) late expressers (SSII-3, III-2, GBSSI), which are expressed in the mid to later stage of grain filling; and (iii) steady expressers (SSI, II-1, IV-1, IV-2), which are expressed relatively constantly during grain filling. Within a caryopsis, the three gene groups spatially share their expression, i.e. ‘‘early expressers’’ in the pericarp, the “late expressers’’ in the “endosperm’’ and the ‘‘steady expressers’’ in both tissues. In addition, this grouping was reflected in the expression pattern of various rice tissues: expression in non-endosperm, endosperm or all tissues examined. The implications in this spatio-temporal work sharing of starch synthesis isogenes are discussed.

Evolution

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You can also add sub-section(s) at will. A rice (Oryza sativa 1.) genomic clone encoding the gene for a form of soluble starch synthase (SSS1) and its 5’- and 3’-flanking regions has been isolated and sequenced. The SSSl gene contained 15 exons interrupted by 14 introns. The exon/intron organization of the SSSl gene was divergent from that of the rice Waxygene coding for granule-bound starch synthase, thus suggesting that the SSSl and granule-bound starch synthase genes have evolved from an ancestral gene in a different way or that the two genes are products of different ancestral genes that have converged during evolution. However, these two genes were closely located to each other on rice chromosome 6 at an approximate map distance of 5 centimorgans. The nucleotide sequence of the 5’-end region of the gene is unique because of the presence of some repetitive sequences.

Labs working on this gene

Please input related labs here. Department of Biological Production, Akita Prefectural University, Akita City, Akita 010–0195, Japan(N.F., M.Y., N.A., T.O., Y.N.); Core Research for Evolutional Science and Technology, Japan Science and Technology, Kawaguchi, Saitama 332–0012, Japan (N.F., M.Y., T.O., Y.N.); and National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305–8602, Japan (A.M., H.H.)

References

Please input cited references here. Function and Characterization of Starch Synthase I Using Mutants in Rice. Plant Physiology, 2006, 140(3): 1070-1084 Compensation and interaction between RISBZ1 and RPBF during grain filling in rice.The Plant Journal, 2009, 59(6): 908-920 Structure, Organization, and Chromosomal Location of the Gene Encoding a Form of Rice Soluble Starch Synthase Plant Physiology, 1995, 108(2): 677-683 Comprehensive Expression Analysis of the starch synthase gene family in rice (Oryaza sativa L.) Planta, 2004, 220(1): 9-14