Characterization of three Arabidopsis AP2/EREBP family transcription factors involved in ABA sensitivity, freeze and salt tolerance

Abstract

AP2/EREBP transcription factors (TFs) play very important roles in plant development, hormonal regulation and stress response. Upon genome-wide cDNA cloning, phylogenetic and expression pattern analyses of this plant specific TF family, we found that three of the members including At1g71450, At1g50680 and At5g13910, were likely involved in responses to ABA, cold and salt. Complementary DNAs containing putative full-length ORFs of these three TFs were obtained and fused individually to the GAL4 DNA-binding domains. All the 3 genes functioned effectively as trans-activators using yeast one-hybrid assays. RT-PCR experiments showed that the At1g71450 gene was induced by ABA and low temperature; the At1g50680 gene was responsive to quite a few stress conditions, but especially to freezing temperature; and the At5g13910 gene was induced by high salt treatment, drought and ethylene. By searching the ABRC T-DNA insertion mutant stocks, we obtained knockout lines for these TFs. Homozygous ko1 (At1g71450) plants showed a hypersensitive response to ABA during seed germination and also in stomata movement. Homozygous ko2 (At1g50680) plants showed a significant reduction in plant freezing tolerance compared to the wild type after chilling treatment. Homozygous ko3 (At5g13910) were less tolerant to high salinity than wild type plants. Our data suggest that At1g71450 is a negative regulator in ABA signaling, while At1g50680 and At5g13910 are positive regulators in cold and salt stress responses, respectively.