Genome-wide characterization of the WRKY gene family in Juglans mandshurica and expression profiling of JmWRKY51 under drought stress

WRKY transcription factors are plant-specific regulators involved in plant growth, development, and responses to environmental stresses. However, the WRKY gene family and its potential roles in drought responses remain insufficiently characterized in Juglans mandshurica . In this study, a genome-wide analysis identified 89 non-redundant JmWRKY genes, which were systematically characterized based on phylogenetic relationships, conserved motifs, gene structures, chromosomal distributions, promoter cis-acting elements, and gene duplication patterns. Phylogenetic analysis classified JmWRKY proteins into three major groups, while collinearity and selection-pressure analyses indicated that segmental duplication contributed substantially to JmWRKY family expansion and that duplicated gene pairs were predominantly subjected to purifying selection. Transcriptome analysis and quantitative real-time polymerase chain reaction validation identified several drought-responsive JmWRKY genes. Among them, JmWRKY51 was significantly induced by drought treatment and contained multiple stress- and hormone-responsive cis-acting elements in its promoter. A β-glucuronidase reporter assay further showed enhanced JmWRKY51 promoter activity under drought stress. Protein-protein interaction prediction suggested that JmWRKY51 may participate in a drought-associated regulatory network. These findings provide a comprehensive characterization of the WRKY gene family in J. mandshurica and identify JmWRKY51 as a promising candidate for further investigation of drought stress tolerance mechanisms.