Genome-wide identification and characterization of cysteine-rich polycomb-like protein (CPP) family genes in cucumber (Cucumis sativus) and their roles in stress responses

Cysteine-rich polycomb-like protein (CPP) transcription factors are a small gene family involved in the regulation of plant growth, development and stress response. Genome-wide identification and characterization of CPP gene family have been carried out in several plant species. However, no comprehensive phylogenetic analysis or expression profiling of CPP genes in Cucumis sativus has been reported. In this study, we characterized the CPP family genes in C. sativus, and 5 CPP candidate genes were found in cucumber genome. CPP proteins from cucumber and other plant species were classified into two groups, which were further divided into five subgroups based on the phylogenetic distribution. Most CPP genes in the same subgroup shared similar gene structures and conserved motifs. Transcriptome data revealed that CsCPP genes were expressed in leaves, ovaries, flowers, stems, roots, and tendril tissues. qRT-PCR expression analysis showed that many CsCPP genes exhibited different expression patterns in cucumber leaves under abiotic stresses including salt, cold, drought, and ABA. These results demonstrate that cucumber CPP gene family may play critical roles in plant development as well as in the responses to environmental stresses.