Identification and expression of the CEP gene family in apple (Malus×domestica)

Plant peptide hormones play important roles in plant growth and development. Among these hormones, the C-TERMINALLYENCODED PEPTIDE (CEP) belongs to a newly found peptide family that regulates root development in Arabidopsis as well as in other species. However, nothing is known about the CEP genes in apple (Malus×domestica, MdCEP). In this study, a total of 27 apple CEP genes were identified through a genome-wide analysis and were phylogenetically divided into three classes (I, II and III). The predicted MdCEP genes were distributed across 10 of 17 chromosomes with different densities. Next, the gene structures and motif compositions of the MdCEP genes were analyzed. Subsequently, the expression analysis suggested that the MdCEP genes were highly activated in roots and that MdCEP23 may play an important role in regulating the growth and development of roots. Moreover, all of the MdCEP genes were responsive to multiple abiotic stresses, indicating that MdCEP genes may be involved with various aspects of physiological processes in apple. Nearly one-third of MdCEP genes had a significant response to low nitrogen treatment. Most of the MdCEP genes were up-regulated under stress, including mannitol, polyethylene glycol (PEG) and abscisic acid (ABA), suggesting that MdCEP genes may be involved in the drought stress response. This study provides insight into the putative functions of the MdCEP genes using a genome-wide analysis of the CEP gene family.