Genome-Wide Identification and Expression Pattern Analysis of the WNK Gene Family in Apple under Abiotic Stress and Colletotrichum siamense Infection

With-no-lysine kinase (WNK) is a unique serine/threonine kinase family member. WNK differs from other protein kinases by not having a standard lysine in subdomain II of the universally preserved kinase catalytic region. Conversely, the amino acid lysine located in subdomain I plays a crucial role in its phosphorylation. The WNK family has been reported to regulate <i>Arabidopsis</i> flowering, circadian rhythm, and abiotic stress. Eighteen members of the <i>WNK</i> gene family were discovered in apples in this research, and they were primarily grouped into five categories on the phylogenetic tree. Conserved domains and motifs also confirmed their identity as members of the WNK family. Promoter cis-acting element analysis indicated their potential role in responses to both abiotic stress and phytohormones. Furthermore, qRT-PCR analysis showed that the expression of <i>MdWNK</i> family genes was stimulated to different extents by <i>Colletotrichum siamense</i>, NaCl, mannitol, ABA, JA, and SA, with <i>Colletotrichum siamense</i> being the most prominent stimulant. <i>MdWNK</i> family genes were expressed across all apple tissues, with young fruits showing the greatest expression and roots showing the least expression. The research offered detailed insights into the <i>MdWNK</i> gene family, serving as a crucial basis for investigating the biological roles of <i>MdWNK</i> genes.