Rice FERONIA-LIKE RECEPTOR 3 and 14 affect grain quality by regulating redox homeostasis during endosperm development

Chalky endosperm negatively affects the appearance, milling, and eating qualities of rice (Oryza sativa L.) grains. Here, we report the role of two receptor-like kinases, FERONIA-LIKE RECEPTOR 3 (FLR3) and FERONIA-LIKE RECEPTOR 14 (FLR14), in grain chalkiness and quality. Knockouts of FLR3 and/or FLR14 increased the number of white-core grains caused by aberrant accumulation of storage substances, resulting in poor grain quality. Conversely, the overexpression of FLR3 or FLR14 reduced grain chalkiness and improved grain quality. Transcriptome and metabolome analyses showed that genes and metabolites involved in the oxidative stress response were significantly up-regulated in flr3 and flr14 grains. The content of reactive oxygen species was significantly increased in flr3 and flr14 mutant endosperm but decreased in overexpression lines. This strong oxidative stress response induced the expression of programmed cell death (PCD)-related genes and caspase activity in endosperm, which further accelerated PCD, resulting in grain chalkiness. We also demonstrated that FLR3 and FLR14 reduced grain chalkiness by alleviating heat-induced oxidative stress in rice endosperm. Therefore, we report two positive regulators of grain quality that maintain redox homeostasis in the endosperm, with potential applications in breeding rice for optimal grain quality.