Identification and characterization of cysteine-rich polycomb-like protein (CPP) gene family in rice (Oryza sativa L.) in response to phytohormones and Xanthomonas oryzae pv. oryzae stress

Cysteine-rich polycomb-like proteins (CPPs) are found in both monocotyledonous and dicotyledonous plants. These CPPs are part of nine various families of proteolytic enzymes, and they play a crucial role in various physiological, especially defence mechanisms. Nevertheless, there is a lack of findings regarding the function of CPPs in disease resistance in rice (Oryza sativa). We recently discovered eleven CPPs in the rice genome. They can be divided into three clades: I, II, and III along with CPPs from other plants like Arabidopsis thaliana (eight members), Cucumis sativus (five members), and Glycine max (thirteen members) based on their phylogenetic relationships. It is interesting to observe how segmental duplication (SD) has assisted the emergence of the OsCPP genes in rice, whereas no evidence of tandem duplication (TD) has been detected. Synteny analyses revealed three pairs of orthologous CPP genes amongst O. sativa and A. thaliana, as well as three pairs between O. sativa and C. sativus. These OsCPPs possess ten conserved amino acid motifs and several exons and introns, as determined by their gene structures. Additionally, they possess distinctive domains such as TCR and TCR superfamily domains. Cis-regulatory elements identified in the OsCPP promoter sequences were shown to be sensitive to auxin, abscisic acid, gibberellins, salicylic acid, methyl jasmonate, and light. Furthermore, stress-responsive elements and tissue-specific expression elements were identified. A large number of OsCPP genes are expressed in different kinds of tissues and organs. Several of these genes are induced by abscisic acid and jasmonic acid. Moreover, specific OsCPP genes are stimulated by Xanthomonas oryzae pv. oryzae (Xoo), the pathogen responsible for bacterial leaf blight in rice. In particular, the pathogen causes a notable overexpression of OsCPP9, suggesting its potential involvement in the plant's defense system. These results highlight the possible contributions of OsCPP genes to rice resistance against Xoo disease.