AtbZIP62 Acts as a Transcription Repressor to Positively Regulate ABA Responses in Arabidopsis.

The basic region/leucine zipper (bZIP) transcription factor AtbZIP62 is involved in the regulation of plant responses to abiotic stresses, including drought and salinity stresses, NO transport, and basal defense in Arabidopsis. It is unclear if it plays a role in regulating plant responses to abscisic acid (ABA), a phytohormone that can regulate plant abiotic stress responses via regulating downstream ABA-responsive genes. Using RT-PCR analysis, we found that the expression level of was increased in response to exogenously applied ABA. Protoplast transfection assays show that AtbZIP62 is predominantly localized in the nucleus and functions as a transcription repressor. To examine the roles of AtbZIP62 in regulating ABA responses, we generated transgenic Arabidopsis plants overexpressing and created gene-edited mutants using CRISPR/Cas9. We found that in both ABA-regulated seed germination and cotyledon greening assays, the transgenic plants were hypersensitive, whereas mutants were hyposensitive to ABA. To examine the functional mechanisms of AtbZIP62 in regulating ABA responses, we generated Arabidopsis transgenic plants overexpressing , and performed transcriptome analysis to identify differentially expressed genes (DEGs) in the presence and absence of DEX, and found that DEGs are highly enriched in processes including response to abiotic stresses and response to ABA. Quantitative RT-PCR results further show that AtbZIP62 may regulate the expression of several ABA-responsive genes, including , and . In summary, our results show that is an ABA-responsive gene, and AtbZIP62 acts as a transcription repressor to positively regulate ABA responses in Arabidopsis.