A mitochondrion-associated PPR protein, WBG1, regulates grain chalkiness in rice.

Rice kernel quality has vital commercial value. Grain chalkiness deteriorates rice's appearance and palatability. However, the molecular mechanisms that govern grain chalkiness remain unclear and may be regulated by many factors. In this study, we identified a stable hereditary mutant, (), which has a white belly in its mature grains. The grain filling rate of was lower than that of the wild type across the whole filling period, and the starch granules in the chalky part were oval or round and loosely arranged. Map-based cloning showed that was an allelic mutant of , which encodes a mitochondrion-targeted P-type pentatricopeptide repeat protein. Amino acid sequence analysis found that two PPR motifs present in the C-terminal of WBG1 were lost in wbg1. This deletion reduced the splicing efficiency of intron 1 to approximately 50% in , thereby partially reducing the activity of complex I and affecting ATP production in grains. Furthermore, haplotype analysis showed that was associated with grain width between and rice varieties. These results suggested that influences rice grain chalkiness and grain width by regulating the splicing efficiency of intron 1. This deepens understanding of the molecular mechanisms governing rice grain quality and provides theoretical support for molecular breeding to improve rice quality.