OsPCK1 regulates photosynthate transport from source to sink and affects grain filling in rice

Ensuring global food security hinges on increasing rice ( Oryza sativa L.) yield, and grain-filling is a primary determinant of key yield components such as grain size and weight. Phospho enol pyruvate carboxykinase (PEPCK), encoded by the PCK gene (LOC_Os03g15050), has been identified in C 3 plants including rice, however, its biological roles and regulatory networks remain poorly understood in the absence of a complete C 4 photosynthetic apparatus. As a pivotal enzyme in gluconeogenesis, PEPCK may be intimately involved in carbon partitioning and the mobilization of photosynthetic products during grain filling. To investigate the functional mechanism of OsPCK1 (a transcript of rice PCK) Oryza sativa L. ssp. japonica Nipponbare (wild type, WT), the OsPCK1 knockout mutant ( ospck1 ), and overexpression lines ( OX10 , OX15 ) were employed as experimental materials. Through integrated phenotypic characterization, physiological measurements, and molecular analyses, we demonstrated that OsPCK1 positively regulated the expression of genes controlling panicle architecture and grain morphology. Additionally, OsPCK1 may play a role in facilitating the translocation of photoassimilates to reproductive organs, by upregulating key genes associated with sugar transport ( OsSUTs , OsSWEETs ) and starch biosynthesis ( OsAGPS1 , OsAGPL1 ), thereby improving yield-related traits. Conversely, the loss of OsPCK1 function resulted in significant downregulation of these genes, leading to compromised panicle fertility with reduced grain number and decreased 1000-grain weight. Our results suggest that OsPCK1 may regulate carbon allocation by concurrently influencing photosynthetic carbon assimilation and starch accumulation in grains, thereby contributing to sugar transport and starch biosynthesis during grain filling. These findings offer new insights into PEPCK function in C 3 plants and may provide a reference for future strategies aimed at increasing rice yield by optimizing carbon allocation.