Genome-wide identification of PLCPs in pepper and the functional characterization of CaCP34 in resistance to salt- and osmotic-induced leaf senescence

The papain-like cysteine proteases (PLCPs) family contains many proteolytic enzymes involved in plant growth and development, leaf senescence, immunity, and stress responses. However, little is known about these enzymes in pepper. We identified 35 PLCPs, which were divided into nine subfamilies based on evolution phylogeny, including four RD21 (responsive to desiccation 21), two CEP (cysteine endopeptidase), two XCP (xylem cysteine peptidase), three XBCP3 (xylem bark cysteine peptidase 3), one THI, ten SAG12 (senescence-associated gene 12), three RD19 (responsive to desiccation 19), one ALP (aleurain-like protease) and eight CTB (cathepsin B-like). The identities of PLCPs were revealed by analyzing conserved motifs, domains and gene structures. An analysis of the putative promoter regions (2 kb upstream regions of the start codon) revealed the enrichment of plant growth, environmental stress and phytohormone signaling cis-elements. Expression profiling revealed diverse patterns of CaPLCPs family members over various tissues. Transcriptional profiling showed a distinct pattern of expression under abiotic stress. Silencing CaCP34 promoted leaf senescence induced by salt and osmotic stress. In contrast, CaCP34 overexpression enhanced the tolerance of pepper to leaf senescence induced by salt and osmotic stress. Taken together, these results demonstrate that the CaPLCPs have various roles in developmental senescence and resistance in pepper.