Genome-Wide Characterization of the Mitogen-Activated Protein Kinase Gene Family and Their Expression Patterns in Response to Drought and Colletotrichum Gloeosporioides in Walnut ().

Mitogen-activated protein kinases (MAPKs) are a family of Ser/Thr (serine/threonine) protein kinases that play very important roles in plant responses to biotic and abiotic stressors. However, the MAPK gene family in the important crop walnut ( L.) has been less well studied compared with other species. We discovered 25 members in the genome in this study. The gene family was separated into four subfamilies based on phylogenetic analysis, and members of the same subgroup had similar motifs and exons/introns. A variety of cis-acting elements, mainly related to the light response, growth and development, stress response, and hormone responses, were detected in the gene promoters. Collinearity analysis showed that purification selection was the main driving force in gene evolution, and segmental and tandem duplications played key roles in the expansion of the gene family. The RNA-Seq (RNA Sequencing) results indicated that many of the genes were expressed in response to different levels of infection. , , , , , , , , , , , , , and were upregulated at the transcriptional level in response to the drought stress treatment. The results of this study will help in further investigations of the evolutionary history and biological functions of the MAPK gene family in walnut.