Drought stress critically impacts plant growth and productivity. The bZIP transcription factor family is crucial for abiotic stress responses, yet its role in larch drought tolerance remains unclear. This study identified 19 bZIP genes in Larix kaempferi (Lamb.) Carr. and characterized LkbZIP4. Bioinformatics analysis classified it into the A subgroup. Subcellular localization and yeast two-hybrid assays confirmed that it is a nucleus-localized transactivator. Expression pattern analysis revealed that LkbZIP4 was highly specifically expressed in roots and was significantly induced by drought stress. A series of transgenic overexpression lines was successfully established through Agrobacterium tumefaciens-mediated method, using embryogenic callus of hybrid larch (L. kaempferi × L. gmelinii). Under 7% PEG-induced drought stress, LkbZIP4-overexpressing transgenic calli displayed enhanced drought tolerance relative to wild-type. This was evidenced by better growth, higher biomass, and reduced membrane damage, indicated by lower malondialdehyde content and relative electrolyte leakage. Meanwhile, these transgenic calli accumulated higher levels of osmoregulatory substances, including proline and soluble sugars, along with enhanced activities of antioxidant enzymes including superoxide dismutase and peroxidase. Our results indicate that LkbZIP4 functions to promote drought tolerance in larch, likely through the enhancement of osmotic adjustment and oxidative defense mechanisms.
Zhang et al. (Sun,) studied this question.