PagBEH3b regulates water maintenance and reactive oxygen species scavenging to control poplar drought tolerance

The BES/BZR transcription factor BEH3 protein is important for regulating and stabilizing vascular tissue development in Arabidopsis. However, the biological functions of poplar BEH3 genes, the homologs of AtBEH3 in poplar, remain unexplored. In this study, four BEH3 genes from Populus, with PagBEH3b exhibiting the highest amino acid sequence similarity to AtBEH3, were identified. Expression analysis revealed that PagBEH3b was predominantly expressed, with the highest level observed in the roots than in those of the other members. Further analysis revealed that PagBEH3b was strongly induced by drought stress. Physiological analyses of PagBEH3b overexpression (PagBEH3b OE) and PagBEH3b-knockout (Pagbeh3) transgenic poplar plants revealed that PagBEH3b OE plants had a greater tolerance to drought stress, whereas Pagbeh3 were more sensitive. The altered tolerance to drought stress was closely associated with increases or decreases in stomatal aperture, water use efficiency, antioxidant enzyme activities, and expression of antioxidant enzyme-encoding genes in PagBEH3b OE and Pagbeh3 transgenic poplar plants. These results highlight the key role of PagBEH3b in drought stress responses and its promising potential for the breeding of new tree cultivars with increased tolerance to abiotic stress.