Identification of the CDPK Pan-Genomic Family in Pear (Pyrus spp.) and Analysis of Its Response to Venturia nashicola

This study investigated the phylogenetic relationships in the pear calcium-dependent protein kinase (CDPK) pan-gene family and elucidated its role in the resistance to scab disease caused by Venturia nashicola. By integrating data from eight genomic sets from five cultivated pear species, Pyrus bretschneideri, P. ussuriensis, P. sinkiangensis, P pyrifolia, and P. communis, along with P. betulifolia and interspecific hybrids, 63 PyCDPK family members were identified. Among these, P. communis possessed the highest number of CDPK genes, whereas P. bretschneiderilia had the fewest. These genes encode proteins ranging from 459 to 810 amino acids in length, and are predominantly localized to the cell membrane. Six genes, PyCDPK9, PyCDPK11, PyCDPK12, PyCDPK14, PyCDPK16, and PyCDPK19, were classified as core members of the pan-genome, and PyCDPK19 showed evidence of positive selection pressure. Clustering analysis and transcriptomic expression profiling of disease-resistance-related CDPKs identified PyCDPK19 as a key candidate associated with scab resistance. Promoter analysis revealed that the regulatory region of PyCDPK19 contains multiple cis-acting elements involved in defense responses and methyl jasmonate signaling. Transient overexpression of PyCDPK19 in tobacco leaves induced hypersensitive cell necrosis, accompanied by significant increases in hydrogen peroxide (H2O2) accumulation and malondialdehyde (MDA) content. Similarly, overexpression in pear fruit callus tissue followed by pathogen inoculation resulted in elevated levels of both H2O2 and MDA. Collectively, these findings indicate that PyCDPK19 mediates defense responses through the activation of the reactive oxygen species pathway in both tobacco and pear plants, providing a promising genetic target for enhancing scab resistance in pears.