OsLESV and OsESV1 promote transitory and storage starch biosynthesis to determine rice grain quality and yield

Abstract

Transitory starch is an important carbon source in leaves, and its biosynthesis and metabolism are closely related to grain yield and quality. The molecular mechanisms controlling leaf transitory starch biosynthesis and degradation and their effects on rice (Oryza sativa) yield and quality are unclear. Here, we showed that OsLESV and OsESV1, the rice orthologs of AtLESV and AtESV1, are associated with transitory starch biosynthesis in rice. The total starch and amylose contents in leaves and endosperm were significantly reduced, and the final grain quality and yield were compromised in oslesv and osesv1 single and oslesv esv1 double mutants. Further, we found that OsLESV and OsESV1 bind to starch and that this binding depends on a highly conserved C-terminal tryptophan-rich region that acts as a starch-binding domain. Importantly, OsLESV and OsESV1 also interact with the key enzymes of starch biosynthesis, GBSSI, GBSSII, and PPDKB, and maintain their protein stability and activity levels. OsLESV and OsESV1 also assist in targeting GBSSI and GBSSII from plastid stroma to starch granules. Overexpressing GBSSI, GBSSII, and PPDKB partly rescued the phenotypic defects of the oslesv and osesv1 mutants. Thus, we demonstrated that OsLESV and OsESV1 play a key role in regulating the biosynthesis of both leaf transitory starch and endosperm storage starch in rice. These findings enhance our understanding of the molecular mechanisms underlying transitory starch biosynthesis in rice leaves and reveal how transitory starch metabolism affects rice grain quality and yield, providing useful information for the genetic improvement of rice grain quality and yield.