Abstract
Grain size and weight are two important determinants of grain yield in rice. Although overexpression of sucrose synthase (SUS) genes has led to several improvements on cellulose and starch-based traits in transgenic crops, little is reported about SUS enhancement of hull size and grain weight in rice. In this study, we selected transgenic rice plants that overexpressed OsSUS1-6 genes driven with the maize Ubi promoter. Compared to the controls (wild type and empty vector line), all independent OsSUS homozygous transgenic lines exhibited considerably increased grain yield and grain weights. Using the representative OsSUS3 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 OsSUS3 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 OsSUS overexpression could significantly improve hull size and grain weight by dynamically regulating cell division and starch accumulation in the transgenic rice.
Highlights
Rice is one of the major staple food crops over the world
Because there are seven sucrose synthase (SUS) isoforms in rice and OsSUS7 exhibits 99% similarity with OsSUS5 [37], this study did not perform any investigation of OsSUS7
According to the phylogenetic analysis, the SUS family were classified into four distinct clades in plants: Clade I were of dicot members; Clade II contained monocot members including rice OsSUS1, OsSUS2, and OsSUS3; Clade III and IV consisted of both monocot and dicot members with OsSUS4, OsSUS5, and OsSUS6, respectively (Table S1, Figure 1B)
Summary
Rice is one of the major staple food crops over the world. Grain size and weight are tightly associated with grain yield in rice. Grain length, width and thickness basically determine grain size, while hull size and degree of grain filling are key agronomic traits in determining grain weight [1]. Large number of QTLs for rice size and weight have been identified [2], and several major genes are relatedly characterized. Genetic manipulation specific for concurrent improvements of both hull size and grain weight in rice remains to be explored
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