Abscisic acid (ABA) plays an important role in seed germination, stomatal closure, and seedling growth inhibition in plants. Among downstream genes whose expression levels are regulated by AFA1 (Arabidopsis F-box Protein Hypersensitive to ABA 1), one gene, AtHAD1 upregulated by ABA was selected from Arabidopsis. AtHAD1 was induced by drought and salt stresses as well as by ABA and was found in dry seeds. Its loss-of-function mutants exhibited increased ABA-sensitivity in germination, seedling growth, and stomatal closure. In addition, the mutants displayed a lower water loss rate and higher survival rate under drought stress than the wild-type plants, indicating that a loss of AtHAD1 leads to enhanced drought tolerance. These results show that AtHAD1 has an inhibitory role in the ABA response and ABA-mediated drought tolerance. The expression levels of several ABA-responsive genes in athad1 were higher than those in the wild-type under the ABA treatment, suggesting that AtHAD1, as a negative regulator in the ABA response, could be associated with the downregulation of the ABA-responsive genes. The phosphatase assay showed that AtHAD1 exhibits phosphatase activity. Monitoring of the subcellular localization of GFP-fused AtHAD1 proteins indicated that AtHAD1 exists in the nucleus and cytoplasm. Overall, this study shows that Arabidopsis HAD1 as an intracellular phosphatase negatively functions in the ABA-mediated cellular responses. This research could serve as a research basis to understand the functional link between ABA signaling and the regulation process of the cellular phosphate level.
Keywords: A negative regulator; ABA response; Arabidopsis; AtHAD1; Drought tolerance.
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