Genome-wide identification of the SnRK2 gene family and its response to drought stress in Bombax ceiba

Abstract

Introduction Drought is a major abiotic stress limiting the growth and ecological adaptation of tropical and subtropical trees. The SnRK2 gene family is a core regulator in ABA signaling and drought response pathways. However, genome-wide identification and functional characterization of the SnRK2 family remain unclear in Bombax ceiba, a typical drought-tolerant tropical pioneer tree species with important ecological and economic value. Methods We performed genome-wide identification of the BcSnRK2 gene family using bioinformatics approaches. Phylogenetic relationships, gene structures, conserved motifs, cis-acting elements, chromosomal localization, and protein structures were systematically analyzed. Subcellular localization was verified by transient expression in Nicotiana benthamiana. Tissue-specific expression and drought-responsive patterns were detected by qRT-PCR under 10% PEG6000 treatment. Protein–protein interaction networks were predicted using the STRING database. Results A total of nine BcSnRK2 genes were identified and unevenly distributed across eight chromosomes. All BcSnRK2 proteins contained conserved kinase domains and shared a highly conserved exon–intron structure. Promoter regions harbored abundant ABA-responsive and stress-related cis-elements. BcSnRK2 genes exhibited distinct tissue-specific expression profiles. All genes were significantly induced by drought stress in a tissue- and time-dependent manner, with BcSnRK2.9 and BcSnRK2.7 showing strong and sustained activation in shoots and BcSnRK2.7 and BcSnRK2.3 responding prominently in roots. BcSnRK2 proteins were localized in the cytoplasm, plasma membrane, and nucleus, and were predicted to interact with core components of the ABA signaling pathway. Discussion The BcSnRK2 family exhibits evolutionary conservation and functional divergence in Bombax ceiba. The compact size of the SnRK2 family, conserved structural features, and distinct tissue-specific drought response patterns are consistent with a streamlined stress signaling system that may contribute to the ecological adaptation of Bombax ceiba in seasonally dry tropical environments, although formal evolutionary analyses are required to establish adaptive significance. This study provides valuable gene resources for drought resistance breeding of woody plants and advances the understanding of stress signaling mechanisms in tropical trees.