3.4.22.25 evolution all four major papain-like cysteine proteases (PLCPs) purified from papaya latex, including papain, chymopapain, glycyl endopeptidase and caricain, are grouped into the lineage-specific expansion branch in the subfamily III of papain-like cysteine proteases (PLCPs). Tandem duplications play the dominant role in affecting copy number of PLCPs in plants. Significant variations in size of the PLCP subfamilies among species may reflect genetic adaptation of plant species to different environments. The lineage-specific expansion of papaya PLCPs of subfamily III might have been promoted by the continuous reciprocal selective effects of herbivore attack and plant defense. Phylogenetic analysis, conserved domain identification, gene duplication analysis, and chromosomal distribution of PLCPs, overview 753097 3.4.22.25 metabolism papain-like cysteine proteases (PLCPs), a large group of cysteine proteases structurally related to papain, play important roles in plant development, senescence, and defense responses 753097