Sucrose Synthase Enhances Hull Size and Grain Weight by Regulating Cell Division and Starch Accumulation in Transgenic Rice

Grain size and weight are two important determinants of grain yield in rice. Although overexpression of sucrose synthase ( ) genes has led to several improvements on cellulose and starch-based traits in transgenic crops, little is reported about enhancement of hull size and grain weight in rice. In this study, we selected transgenic rice plants that overexpressed genes driven with the maize Ubi promoter. Compared to the controls (wild type and empty vector line), all independent homozygous transgenic lines exhibited considerably increased grain yield and grain weights. Using the representative overexpressed transgenic plants, four independent homozygous lines showed much raised cell numbers for larger hull sizes, consistent with their enhanced primary cell wall cellulose biosynthesis and postponed secondary wall synthesis. Accordingly, the transgenic lines contained much larger endosperm volume and higher starch levels than those of the controls in the mature grains, leading to increased brown grain weights by 15-19%. Hence, the results have demonstrated that overexpression could significantly improve hull size and grain weight by dynamically regulating cell division and starch accumulation in the transgenic rice.