Arabidopsis Cys2/His2 Zinc-Finger Proteins AZF1 and AZF2 Negatively Regulate Abscisic Acid-Repressive and Auxin-Inducible Genes under Abiotic Stress Conditions

In plants, abiotic stresses induce various physiological changes and growth inhibition that result in adaptive responses to these stresses. However, little is known about how such stresses cause plant growth inhibition. Many genes have been reported to be repressed in plants under abiotic stress conditions. ZPT2 (for petunia [Petunia hybrida] zinc-finger protein 2)-related proteins with two Cys2/His2-type zinc-finger motifs and an ethylene-responsive element binding factor-associated amphiphilic repression motif are thought to function as transcriptional repressors. To characterize the roles of this type of transcriptional repressor under abiotic stress conditions, we analyzed the functions of two Arabidopsis (Arabidopsis thaliana) ZPT2-related genes that were induced by osmotic stress and abscisic acid: AZF1 (for Arabidopsis zinc-finger protein 1) and AZF2. The nuclear localization of these two proteins was observed in the roots under control conditions, and the accumulation of AZF2 was clearly detected in the nuclei of leaf cells under stress conditions. Transgenic plants overexpressing AZF1 and AZF2 were generated using stress-responsive promoters or the GVG chemical induction system. The overexpression of these genes caused severe damage to plant growth and viability. Transcriptome analyses of the transgenic plants demonstrated that AZF1 and AZF2 repressed various genes that were down-regulated by osmotic stress and abscisic acid treatment. Moreover, many auxinresponsive genes were found to be commonly down-regulated in the transgenic plants. Gel mobility shift assays revealed that both the AZF1 and AZF2 proteins bound to the promoter regions of these down-regulated genes. These results indicate that AZF1 and AZF2 function as transcriptional repressors involved in the inhibition of plant growth under abiotic stress conditions.