Roles of FERONIA-like receptor genes in regulating grain size and quality in rice.

Grain yield and quality are critical factors that determine the value of grain crops. In this study, we analyzed the functions of 12 FERONIA-like receptor (FLR) family members in rice and investigated their effects on grain size and quality. We found that FLR1, FLR2 and FLR8 negatively regulated grain size, and FLR15 positively regulated grain size. flr1 mutants had a higher cell number and an accelerated rate of grain filling compared to wild-type plants, which led to grains with greater widths. A mechanism underlying the regulation of grain size by FLR1 is that FLR1 is associated with OsRac1 Rho-like GTPase, a positive regulator of grain size. Regarding grain quality, the flr1 mutant had a higher percentage of chalkiness compared with wild-type plants, and seeds carrying mutations in flr3 and flr14 had endosperms with white floury cores. To elucidate the possible mechanism underlying this phenomenon, we found that FLR1 was constitutively expressed during endosperm development. RNA-seq analysis identified 2,367 genes that were differentially expressed in the flr1 mutant, including genes involved in starch and sucrose metabolism and carbon fixation. In this study, we identified the roles played by several FLR genes in regulating grain size and quality in rice and provided insights into the molecular mechanism governing the FLR1-mediated regulation of grain size.