Nuclear factor OsNF-YC5 regulates grain size and quality in rice

OsNF-YC5, a member of the nuclear factor Y (NF-Y) transcription factor family, plays a key role in rice grain development. Expression analysis showed that OsNF-YC5 is highly expressed in young panicles and grains during the grain-filling stage. Knockout of OsNF-YC5 resulted in longer but narrower and thinner grains, with increased length-to-width and length-to-thickness ratios, yet a 15.1% decrease in thousand-grain weight. Scanning electron microscopy revealed that the lemma epidermal cells in the osnf-yc5 mutant underwent longitudinal expansion and transverse contraction, with reduced cell number along the width, likely contributing to the altered grain morphology. Moreover, osnf-yc5 mutant exhibited impaired grain filling, with the chalky grain rate increasing dramatically from 5.5% in the wild type to 81.1%. Composition analysis showed significant content changes in major storage substances, including total starch, amylose, prolamin, glutelin, and total lipid content, which decreased by 14.3%. In contrast, overexpression of OsNF-YC5 resulted in smaller seeds, with reduced grain length, width, thickness, and weight as well as elevated chalky grain rates. Transcriptome profiling identified 1,046 differentially expressed genes (DEGs) in osnf-yc5 mutants, these DEGs were enriched in functions and pathways including regulation of transcription, nutrient reservoir activity, endoplasmic reticulum protein processing, starch and sucrose metabolism, suggesting that OsNF-YC5 is involved in grain filling and storage substance accumulation. These findings underscore the importance of OsNF-YC5 in controlling grain size and quality, highlighting its potential to improve rice production.