Institute of Crop Science and the National Key Facility for Crop Gene Resources and Genetic Improvement, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Genome. 2011 Jun;54(6):448-59. doi: 10.1139/g11-010. Epub 2011 May 19.
Soluble starch synthases (SSs) are major enzymes involved in starch biosynthesis in developing rice (Oryza sativa L.) endosperm. Despite extensive studies of SSs in various plant species including rice, the functional modes of action among multiple SS genes are still not clear. Here, we generated transgenic RNA interference (RNAi) repressed lines for seven of the eight members of the rice SS gene family and studied their effects on starch synthesis and grain formation. Consistent with their expression domains, RNAi repression of genes that encode isozymes SSI, SSIIa, and SSIIIa had strong effects on grain development, whereas no obvious phenotypic changes were observed in transgenic plants with the other SS genes being RNAi repressed, indicating functional redundancies among the genes. To study the potential functional interactions of SS genes, we generated SSIIa/SSIIIa double repression lines whose kernels displayed a chalky kernel appearance and had increased amylose levels, increased pasting temperatures, and decreased viscosities. The double mutation also reduced short (degree of polymerization (DP) 5-6) and long (DP 12-23) amylopectin chain contents in the grain and increased the medium long types (DP 7-11). The nonadditive nature of the double mutation line suggests that SSIIa and SSIIIa interact with each other during starch synthesis. Such interaction may be physical via starch phophorylase as indicated by our pair-wise yeast two-hybrid assays on major starch synthesis enzymes. Collectively, the data showed that SSIIa and SSIIIa play distinctive, but partially overlapping, roles during rice grain starch synthesis. The possibility of extensive redundancy or complementarity among SS isozymes is discussed.
淀粉合酶(SSs)是参与水稻(Oryza sativa L.)胚乳淀粉生物合成的主要酶。尽管对包括水稻在内的各种植物物种中的 SSs 进行了广泛的研究,但多个 SS 基因的功能作用模式仍不清楚。在这里,我们生成了水稻 SS 基因家族的 8 个成员中的 7 个的转基因 RNA 干扰(RNAi)抑制系,并研究了它们对淀粉合成和谷物形成的影响。与它们的表达域一致,编码同工酶 SSI、SSIIa 和 SSIIIa 的基因的 RNAi 抑制对谷物发育有强烈影响,而在用其他 SS 基因进行 RNAi 抑制的转基因植物中没有观察到明显的表型变化,表明这些基因之间存在功能冗余。为了研究 SS 基因的潜在功能相互作用,我们生成了 SSIIa/SSIIIa 双抑制系,其籽粒表现出粉质外观,直链淀粉含量增加,糊化温度升高,黏度降低。双突变还降低了籽粒中短(聚合度(DP)5-6)和长(DP 12-23)支链淀粉链的含量,并增加了中长链类型(DP 7-11)。双突变系的非加性性质表明 SSIIa 和 SSIIIa 在淀粉合成过程中相互作用。这种相互作用可能是物理的,如我们对主要淀粉合成酶进行的两两酵母双杂交实验所示。总的来说,这些数据表明 SSIIa 和 SSIIIa 在水稻籽粒淀粉合成中发挥独特但部分重叠的作用。讨论了 SS 同工酶之间广泛冗余或互补的可能性。