Cell differentiation is a key event in organ development;it involves auxin gradient formation,cell signaling,and transcriptional regulation.Yet,how these processes are orchestrated during leaf morphogenesis is poorly understood.Here,we demonstrate an essential role for the receptor-like kinase OsCR4 in leaf development.oscr4 loss-of-function mutants displayed short shoots and roots,with tiny,crinkly,or even dead leaves.The delayed outgrowth of the first three leaves and seminal root in oscr4 was due to defects in plumule and radicle formation during embryogenesis.The deformed epidermal,mesophyll,and vascular tissues observed in oscr4 leaves arose at the postembryo stage;the corresponding expression pattern of proOsCR4:GUS in embryos and young leaves suggests that OsCR4 functions in these tissues.Signals from the auxin reporter DR5rev:VENUS were found to be altered in oscr4 embryos and disorganized in oscr4 leaves,in which indole-3-acetic acid accumulation was further revealed by immunofluorescence.OsWOX3A,which is auxin responsive and related to leaf development,was activated extensively and ectopically in oscr4 leaves,partially accounting for the observed lack of cell differentiation.Our data suggest that OsCR4 plays a fundamental role in leaf morphogenesis and embryogenesis by fixing the distribution of auxin.