CLE peptides act via the receptor-like kinase CRINKLY 4 in Physcomitrium patens gametophore development

The CLAVATA pathway plays a key role in the regulation of multicellular shoot and root meristems in flowering plants. In Arabidopsis, CLAVATA 3-like signaling peptides (CLEs) act via receptor-like kinases CLAVATA 1 and CRINKLY 4 (CR4). In the moss Physcomitrium patens, PpCLAVATA and PpCR4 were previously studied independently and shown to play conserved roles in the regulation of cell proliferation and differentiation. The plant calpain DEFECTIVE KERNEL 1 (DEK1) has been identified as another key regulator of cell division and cell fate in vascular plants and bryophytes. The functional interaction between CLAVATA, CR4, and DEK1 remains unknown. Here, we show that P. patens crinkly4 and dek1 mutants respond differently to CLE peptide treatments suggesting their distinct roles in the CLAVATA pathway. Reduced CLAVATA-mediated suppression of leafy shoot growth in Delta cr4 mutants indicates that PpCR4 is involved in CLV3p perception, most likely as a receptor. The CLV3p strongly suppressed leaf vein development in Delta cr4 mutants, suggesting that other receptors are involved in these processes and indicating a potential role of PpCR4 in organ sensitization to CLEs.