A G-Protein β Subunit, AGB1, Negatively Regulates the ABA Response and Drought Tolerance by Down-Regulating AtMPK6-Related Pathway in Arabidopsis
The phytohormone abscisic acid (ABA) regulates plant growth and development as well as stress tolerance. To gain more insights into ABA signalling, a population of chemical-inducible activation-tagged Arabidopsis mutants was screened on the basis of the ABA effect on the inhibition of seed germination. Two novel ABA supersensitive mutants ABA supersensitive during germination1 (absg1) and absg2 were characterized as alleles of Dicer-like1 (DCL1) and HEN1, respectively, as microRNA biogenesis genes, and accordingly, these two mutants were renamed dcl1-11 and hen1-16. The dcl1-11 mutant was an ABA hypersensitive mutant for seed germination and root growth. Reverse transcriptase polymerase chain reaction assays revealed that the expression of ABA- and stress-responsive genes was increased in dcl1-11, as compared with the wild type (WT). Furthermore, the germination assay showed that dcl1-11 was also more sensitive to salt and osmotic stress. The hen1-16 mutant also showed supersensitive to ABA during seed germination. Further analysis showed that, among the microRNA biogenesis genes, all the other mutants were not only enhanced in sensitivity to ABA, salt and osmotic stress, but also enhanced the expression of ABA-responsive genes. In addition to the mutants in the microRNA biogenesis, the interruption of the production of crucial components of other small RNA pathways such as dcl2, dcl3 and dcl4 also caused ABA supersensitive during germination.