Mutant phenotypes and comprehensive expression analyses reveal roles for CLAVATA in moss vegetative and reproductive development and fertility

Abstract

AbstractThe CLAVATA pathway regulates meristem size in angiosperms, but bryophytes have distinct meristematic activities to vascular plants, and gametophytic CLAVATA functions are divergent between species. Here we analysed the promoter activities of all CLAVATA peptide and receptor-encoding genes in the mossPhyscomitrium patens, and using mutants, identified requirements for PpCLV1 and PpRPK2 receptors in male and female reproductive development and fertility. In gametophytes, all 12CLAVATAgenes were expressed in foraging filaments (caulonemata) and leaves (phyllids), but most tissues showed highly specific patterns of promoter activity.PpCLE3expression specifically marked gametophyte shoot (gametophore) apical cells andPpCLV1bandPpRPK2expression marked overlapping apical domains. Expression in male (antheridia) and female (archegonia and eggs) reproductive tissues led us to use mutants to identify roles forPpCLV1a, PpCLV1bandPpRPK2in fertility and reproductive development. In sporophytes, the foot was a common site ofPpCLEexpression, and all genes were expressed in stomata. NoPpCLEactivity specifically marked the embryonic apical cells, and embryonicPpCLV1bandPpRPK2expression marked distinct apical and basal domains. Thus,P. patensstem cell activity is likely regulated by different genes in gametophytes and sporophytes, and promoter evolution was a likely driver of diversification of CLAVATA function.Plain language summaryWhilst gene gain and duplication contributed to the origin of land plants and diversification of seed plants, significant gene loss is associated with morphological adaptation in bryophytes. In the moss,Physcomitrium patens,CLAVATAgenes expanded from low ancestral numbers, showing exquisite cell type specificity in expression. Our results suggest co-option of CLAVATA into many different developmental processes during moss evolution.