The Waxy (Wx) gene, which encodes a granule-bound starch synthase I, promotes rapid seed germination and embryo growth in rice by enhancing starch-to-sugar conversion.

Abstract

Efficient seed germination and seedling establishment are vital for achieving high rice yields. These processes are governed by pathways involving stored starch mobilization and sugar utilization. The Waxy (Wx) gene controls amylose content in rice grains, and the premature termination of its transcription determines whether the grain is waxy or non-waxy. While Wx is important for regulating rice eating and cooking quality (ECQ), this study reveals a new function for Wx in mediating brassinosteroid-regulated seed germination. Analysis of Wx-related near-isogenic and transgenic lines revealed that seeds carrying the Wxa allele showed faster germination and superior post-germinative growth than those carrying the wx allele. Enhanced post-germinative growth was associated with increased Wx expression, which significantly boosted amylase activity, leading to extensive starch degradation. Additionally, the higher expression and activity of α-amylase in Wxa seeds resulted in greater efficiency of starch-to-sugar conversion. In vitro embryo culture assays demonstrated that the Wxa allele and glucose acted synergistically to promote plumule growth. Moreover, differential Wx expression influenced abscisic acid biosynthesis and catabolism in germinated seeds. Collectively, these findings suggest that appropriately modifying Wx expression to optimize starch composition could achieve the dual goal of improving both ECQ and germination-related traits in rice breeding.