Genome-Wide Characterization of the DELLA Gene Family in Hevea brasiliensis Reveals Evolutionary Diversification and Potential HbDELLA3/4–HbbHLH25 Interaction

DELLA proteins are central negative regulators of gibberellin signaling and play important roles in plant growth, development, and environmental responses. However, the DELLA gene family has not been systematically characterized in Hevea brasiliensis. Here, we identified members of the HbDELLA protein family in the rubber tree genome and examined their evolutionary relationships, conserved motifs, domain organization, chromosomal distribution, collinearity, expression patterns, and protein interactions using comparative genomics, transcript profiling, and yeast two-hybrid assays. Five HbDELLA proteins were identified. Comparative analysis of DELLA proteins from 14 representative species showed that family size ranged from one to five members and that DELLA proteins contain conserved C-terminal GRAS domains but divergent N-terminal DELLA-related regions. Phylogenetic analyses resolved two major clades, S1 and S2, with HbDELLA3 and HbDELLA4 clustering with AtGAI and AtRGA in subclade S1.1. Collinearity analysis suggested that WGD or segmental duplication contributed mainly to HbDELLA family expansion. HbDELLA genes showed tissue- and developmental-stage-specific expression and distinct temporal responses to gibberellin treatment in flowers. Yeast two-hybrid assays supported interactions of HbDELLA3 and HbDELLA4 with HbbHLH25 in yeast. These findings identify candidate protein associations for further investigation but do not establish their occurrence or regulatory functions in rubber tree cells.