Genome-Wide Identification and Water Stress Response of the WRKY Gene Family in Annamocarya sinensis: An Endangered Plant with an Extremely Small Population

Annamocarya sinensis is a Plant Species with Extremely Small Populations (PSESP) of great ecological and research value. Water conditions serve as a key environmental factor that profoundly shapes its growth, physiological homeostasis and stress adaptation. WRKY transcription factor families constitute the core molecular regulatory modules orchestrating plant responses to water-related stresses and environmental fluctuations. This study performs a systematic identification and bioinformatics analysis of the WRKY gene family in A. sinensis, combined with RT-qPCR to verify and analyze its expression patterns under water stress. The results identified a total of 92 WRKY genes unevenly distributed across 16 chromosomes, classified into three distinct subfamilies with obvious conservation of conserved motifs; the gene promoters were enriched with drought cis-elements, and fragment duplication drove the expansion of the family; this family had a high collinearity with the homologous genes of Arabidopsis thaliana, and its evolutionary function was conserved. RT-qPCR confirmed that AsWRKY3, AsWRKY11, AsWRKY17, AsWRKY53 and AsWRKY72 showed differential expression under water stress and were involved in regulating the processes of drought and waterlogging tolerance. Under drought stress, all five genes exhibited an upregulation trend, albeit with slightly varying response intensities; under waterlogging stress, AsWRKY3 and AsWRKY17 demonstrated strong enhanced responses, AsWRKY11 and AsWRKY53 showed early-response patterns, whereas AsWRKY72 exhibited a downregulation trend. In summary, fragment duplication and family differentiation enhanced the functional diversity of the WRKY family, providing a genetic basis for the adaptation of A. sinensis to changes in water availability. The research findings not only provide crucial theoretical clues for exploring the potential environmental adaptation and molecular evolution mechanisms of extremely small population plants, but also offer essential genetic resources and scientific foundations for species conservation, restoring wild populations, and conducting stress-resistant molecular breeding.