The LBD Transcription Factor ZmLBD33 Confers Drought Tolerance in Transgenic Arabidopsis

Drought stress severely impacts maize productivity, necessitating the exploration of molecular mechanisms underlying drought responses. In maize, while Class I members of the LBD family have been extensively studied for their essential functions in developmental regulation and environmental stress responses, the potential involvement of Class II LBD genes in abiotic stress tolerance mechanisms remains poorly characterized. This study characterizes ZmLBD33, a maize Class II LBD gene, to elucidate its role in drought responses. Promoter analysis identified ABA-responsive cis-elements (AREB); ZmLBD33 expression was strongly induced in roots under drought and ABA treatments, localized to the nucleus, and exhibited dimerization via yeast two-hybrid despite lacking intact leucine zipper motifs. ZmLBD33-overexpressed plants showed later germination, shorter roots, and decreased survival rates than wild-type plants under osmotic stress and soil drought. Compared to wild-type plants, ZmLBD33-overexpressed plants showed significantly faster water loss, a greater stomatal density, and reduced stomatal closure efficiency. Histochemical analysis using DAB and NBT showed attenuated reactive oxygen species accumulation in transgenic Arabidopsis overexpressing ZmLBD33. Quantitative enzymatic activity analyses further indicated that SOD and POD levels were significantly elevated in ZmLBD33-overexpressing plants compared to wild-type plants. These findings indicate that ZmLBD33 negatively regulates drought tolerance by modulating stomatal aperture and H₂O₂ signaling. This study highlights the divergent roles of Class II LBD genes in stress adaptation and positions ZmLBD33 as a potential target for engineering drought-resilient crops.