VvLBD39, a grape LBD transcription factor, regulates plant response to salt and drought stress

Grape (Vitis vinifera L.), as an important deciduous perennial fruit tree, constantly confronts various abiotic stresses such as salinity and drought. The lateral organ boundaries domain (LBD) proteins are a class of plantspecific transcription factors that play pivotal roles in regulating plant growth and responding to abiotic stress. However, the biological function of the LBD transcription factor in grape remains poorly understood. Here, we cloned and characterized the VvLBD39 gene from grape, which contained a highly conserved LBD domain and localized to the cell nucleus. qRT-PCR analyses showed that the expression of VvLBD39 was downregulated upon exposure to NaCl, polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA) treatments, respectively. Overexpression of VvLBD39 in grape calli and Arabidopsis resulted in hypersensitivity to PEG6000 and NaCl stress. Moreover, VvLBD39-overexpressing transgenic tobacco exhibited decreased tolerance to drought and salt stress, as well as insensitivity to exogenous ABA. After drought and salt stress treatments, the chlorophyll content, root length and antioxidant enzyme activity of the transgenic tobacco were lower than those of the wildtype (WT). Conversely, malonic dialdehyde (MDA) content, electronic conductivity, hydrogen peroxide (H2O2) content and superoxide anion (O2- ) productivity were markedly elevated in the transgenic tobacco compared to the WT. Further investigations found that VvLBD39 had a negative impact on stomatal closure, ABA biosynthesis and ABA signaling under drought and salt treatments. In addition, the expression of genes related to reactive oxygen species (ROS) scavenging and stress response were significantly downregulated in VvLBD39 transgenic tobacco. Taken together, these results indicated that VvLBD39 functions as a negative regulator of salt and drought tolerance, making it a promising target for drought and salt resistance breeding.