Functional Characterization Of Arabidopsis Transcription Factor TGA7in Plant Responses To Drought Stress

When plants suffer from drought stress, the expression of many genes is regulated, indicating that transcription factors play important roles in plant response to drought stress. There are75members of the bZIP family in Arabidopsis, which are subdivided into ten groups using common domains, and the D group proteins TGAs function in plant defense against pathogens and development. This research work focused on the functional characterization and regulation of AtTGA7in response to drought stress.In our research work, we found the TGA7T-DNA insertion mutant tga7showed a much more tolerant phenotype under drought stress compared with wild-type plant. Complemental experiment showed that tga7mutant complementation line had similar phenotype to the wild-type plant, indicating the function of TGA7in response to drought stress. In contrast, the TGA7-overexpression lines were more susceptible to drought stress compared with wild-type plant. The assay of water loss from detached leaves showed that the tga7mutant lost less water than the wild-type plant and tga7mutant complementation line, while the TGA7-overexpression lines lost much more water than wild-type plant, demonstrated that TGA7may play roles in drought stress. The GUS-staining assay showed that TGA7was preferentially expressed in stomatal guard cell, further stomatal experiments showed that induction of stomatal closure and inhibition of stomatal opening by ABA were impaired in the TGA7-overexpressing lines, indicating that TGA7play roles in plant responses to drought stress by regulating stomatal movement.To find the target genes of TGA7, the expression of ion channel genes, ABA-responsive genes and ABA biosynthesis enzyme genes were tested in the tga7mutant and TGA7-overexpression lines, which were proposed to mediate stomatal movements. qRT-PCR results showed that the expression of AtBG1was strongly repressed in the TGA7-overexpressing lines, further transient expression assay in Nicotiama benthamiana leaves also demonstrated the suppression of AtBGl expression by TGA7.TGA7binds to DNA sequence with an ACGT core (ACE motif), and there are three ACE motifs within the AtBGl promoter. EMSA and ChIP assay demonstrated that TGA7could bind to the AtBG1promoter in vitro and in vivo. Similar to the TGA7overexpression lines, loss-of-function mutant of AtBG1showed drought-sensitive phenotype and was less sensitive to ABA in regulation of stomatal movements. AtBGl expression was markedly induced under drought stress, whereas this induction was restained in the TGA7-overexpression lines.Taken together, our data indicate that TGA7is involved in plant responses to drought stress by negatively regulating AtBGl expression.