OsCHR728 encodes a chromatin remodeling factor involved in seed size and grain chalkiness in rice

The Imitation Switch (ISWI)ATP-dependent chromatin remodeling factor proteins regulate various developmental processes, spanning from flowering to stress response. However, researches on the roles of ISWI subfamily genes in rice have been limited. This study investigated the expression profile of the rice chromatin remodeler OsCHR728, encoding an ISWI protein, across various tissues and developing stages. Our findings reveal that OsCHR728 is highly accumulated during early stage of the panicle development. We generated OsCHR728 knockout (KO) lines in rice using CRISPR/Cas9 technology. These mutant lines displayed smaller grain size compared to the wild type (Zhonghua 11, ZH11). Expression analysis revealed a significant downregulation of the transcript levels of five genes associated with cell cycle regulation in KO grains compared to the wild type, consistent with the reduced cell number in the mutant grains. Additionally, total free amino acid levels were higher in the KO mutant compared to the wild type, consequently enhancing the nutritional quality of the KO mutant grains. The mature endosperm of the KO mutant exhibited a reduced percentage of chalky grains and less chalkiness, suggesting an improvement in the appearance quality of the KO mutant. These results suggest that chromatin remodeling factor OsCHR728 plays a role in grain development, potentially providing a new avenue to enhance both the appearance and nutritional quality of rice cultivars.