Natural variation in OsTPS8 confers differential regulation of chalkiness and seed vigor in indica and japonica rice.

Chalkiness and seed vigor are major agronomic traits affecting rice grain quality and productivity, respectively. Little is known about the intrinsic relationship and the regulatory mechanisms of these two traits. Here we identified a chalkiness locus qPGWC-8, which encodes trehalose-6-phosphate synthase 8 (OsTPS8) that suppresses trehalose-6-phosphate (Tre6P) biosynthesis by interacting with and inhibiting OsTPS1. A natural promoter variation in OsTPS8 confers differential transcriptional regulation by OsbHLH001. Elevated expression of OsTPS8 reduces Tre6P levels and activates the expression of OsMYBS1 and α-amylase genes, thus promoting starch degradation, chalkiness formation and seed vigor elevation. Two major haplotypes, OsTPS8(ASO) and OsTPS8(IR24), were defined by this functional promoter variation, with OsTPS8(IR24) preferentially selected during the domestication of indica rice. Collectively, our findings establish an OsbHLH001-OsTPS8-Tre6P-α-amylase signaling cascade that has a dual role in regulating grain chalkiness and seed vigor, which reveals a molecular link between the appearance quality and seed vigor of rice.