ASR1 and ASR2, Two Closely Related ABA-Induced Serine-Rich Transcription Repressors, Function Redundantly to Regulate ABA Responses in Arabidopsis.

The plant hormone abscisic acid (ABA) is able to regulate the expression of ABA-responsive genes via signaling transduction, and thus plays an important role in regulating plant responses to abiotic stresses. Hence, characterization of unknown ABA response genes may enable us to identify novel regulators of ABA and abiotic stress responses. By using RT-PCR analysis, we found that the expression levels of ()and , two closely related unknown function genes, were increased in response to ABA treatment. Amino acid sequence analyses show that ASR1 contains an L×L×L motif and both ASR1 and ASR2 are enriched in serine. Transfection assays in Arabidopsis leaf protoplasts show that ASR1 and ASR2 were predominantly localized in the nucleus and were able to repress the expression of the reporter gene. The roles of ASRs in regulating ABA responses were examined by generating transgenic Arabidopsis plants over-expressing and respectively, and CRISPR/Cas9 gene-edited single and double mutants for and . In both the seed germination and cotyledon greening assays, ABA sensitivity remained largely unchanged in the over-expression transgenic plants and the single mutants of and , but greatly increased ABA sensitivity was observed in the double mutants. In root elongation assays, however, decreased ABA sensitivity was observed in the : and : transgenic plants, whereas increased ABA sensitivity was observed in the and single mutants, and ABA sensitivity was further increased in the double mutants. Transcriptome analysis show that the differentially expressed genes (DEGs) down-regulated in the : transgenic plant seedlings, but up-regulated in the double mutant seedlings were highly enriched in processes including responses to plant hormones and stress stimuli. Taken together, our results show that and are closely related ABA response genes, ASR1 and ASR2 are serine-rich novel transcription repressors, and they negatively regulate ABA responses in Arabidopsis in a redundant manner.