Utilization of Heterologous Expression of Hvsusiba2 to Increase Grain and Stalk Starch Contents and Amylopectin Synthase Activity in Rice

Hvsusiba2 is a transcription factor acting on the upstream of starch synthesis pathway. It is the key starch synthesis regulator in barley. To understand whether the gene has a similar function in rice, a transgenic homozygous rice line with the barley Hvsusiba2 was created previously. The cultivar was used in this study to compare its starch content and amylopectin synthase activity with the wild type. The results showed that the transgenic line exhibited a higher starch contents in the mature grains and stalks, but not in the leaves or roots, than that in the wild type.Starch accumulation dynamics in the process of grain development were similar between the transgene line and the wild counterpart in the initial 12 days after flowering, but markedly increased 15 days after flowering in the transgenic line. It suggested that Hvsusiba2 might not start affecting the starch synthesis until after mid and late grain filling stages in rice. Furthermore, the activities of amylopectin synthases, such as SBEIIb, SBEI, isoamylase and amylase, were enhanced in the developing grains of transgenic line, but the SBEIIa and pullulanase were not affected by Hvsusiba2. It appeared that the heterologous expression of Hvsusiba2 could increase the starch content, and likely, the activities of several amylopectin synthases as well, in rice similar to what it does in barley.