The IKU2/RLK7–MAPK–MINI3 signaling module controls endosperm cellularization timing to determine seed size in Arabidopsis

variant loses the function of wild-type MINI3 in vivo. Furthermore, we found that IKU2 and RLK7, two closely related receptor-like kinases, function upstream of the MKK4/MKK5-MPK3/MPK6-MINI3 pathway to regulate seed size. The phosphorylation of MINI3 mediated by MPK3/MPK6 enhances its transcriptional activity toward target genes, including IKU2, RLK7, and MINI3 itself, thereby forming a positive regulatory loop within this signaling pathway. In summary, our study elucidates a signaling pathway composed of IKU2/RLK7-MAPKKK(s)-MKK4/MKK5-MPK3/MPK6-MINI3 that regulates endosperm cellularization and seed size, providing a theoretical basis for crop breeding.