CUC genes control boundary domains for shoot meristem maintenance and organ initiation in maize

The proper initiation of lateral organs is crucial for plant growth and crop yield determination. The discovery of the boundary-specific CUP-SHAPED COTYLEDON (CUC) transcription factors provides new insights into this intriguing biological process. Although CUC functions have been extensively studied in eudicots, it is not clear how they control development in monocot crops, such as maize (Zea mays). We identified three maize CUC genes (ZmCUC1, ZmCUC2 and ZmCUC3) that are specifically expressed in the diverse boundary domains of maize and redundantly control leaf separation, shoot apical meristem (SAM) maintenance and axillary meristem (AM) initiation. The three genes have clear functional divergence, with ZmCUC1 and ZmCUC2 primarily regulating leaf margin separation and AM initiation. By contrast, ZmCUC3 plays a broader role, governing the formation of all boundary tissues. All three CUC genes redundantly maintain meristem activity and leaf initiation by regulating multiple pathways, including modulation of the redox regulator MALE STERILE CONVERTED ANTHER1. This study provides direct evidence that CUC genes are crucial for the formation of diverse shoot boundary domains and meristem development in maize, highlighting their roles in the balance between organ initiation and differentiation, and meristem maintenance.