Genome-Wide Identification of MAPK Cascade Genes and Their Expression Patterns in Response to Potato Late Blight

Mitogen-activated protein kinase (MAPK) cascades are conserved signaling modules that regulate plant growth, development, and responses to biotic and abiotic stresses. However, the genome-wide organization and transcriptional responses of the potato MAPK cascade during Phytophthora infestans infection remain insufficiently characterized. In this study, 109 MAPK cascade genes were identified in potato, comprising 17 StMAPKs, five StMAPKKs, and 87 StMAPKKKs. Phylogenetic, chromosomal, gene-structure, and conserved-motif analyses revealed clear family-level conservation, extensive structural diversity among StMAPKKKs, and multiple tandem duplication events. Putative promoter analysis showed that E-box, GT-1 motif, MYB1AT, W-box, and MYC elements were nearly ubiquitous (>95% of genes), whereas TGACG-motif and CGTCA-motif were major potential cis-regulatory elements. Of the 109 genes, 89 were expressed after P. infestans inoculation, including 17 StMAPKs, five StMAPKKs, and 67 StMAPKKKs. Notably, PGSC0003DMG400030058 (MAPK3), PGSC0003DMG401000057 (MAPK4), and PGSC0003DMG400033696 (MAPKK9) were strongly induced, with their expression increasing by 2.3- to 3.5-fold in the incompatible interaction and by 5.0- to 7.4-fold in the compatible interaction, while 13 genes were up-regulated in both incompatible and compatible interactions. Copy-number association analysis detected no significant relationship between any of the 21 examined promoter elements and infection-induced expression after false-discovery-rate correction. These results provide a genome-wide framework for identifying candidate MAPK cascade genes involved in potato-late blight interactions and a basis for subsequent functional validation.