![]() This mechanism might contribute to adaptation by enabling plants to complete their life cycles under drought stress. Taken together, these results suggest that ABF3 and ABF4 act with NF-YCs to promote flowering by inducing SOC1 transcription under drought conditions. Interestingly, the abf3 abf4, nf-yc3 yc4 yc9, and soc1 mutants displayed a reduced drought-escape response. We found that ABF3 and ABF4 interact with nuclear factor Y subunit C (NF-YC) 3/4/9 in vitro and in planta, and induction of SOC1 by ABA was hampered in nf-yc3 yc4 yc9 mutants. 35S:ARR1-SRDX transgenic Arabidopsis plants showed phenotypic changes reminiscent of plants with a reduced cytokinin status, such as a strongly reduced leaf size, an enhanced root system and larger seeds. ABF3 and ABF4 were enriched at the −1028- to −657-bp region of the SOC1 promoter, which does not contain canonical ABF-ABRE-binding motifs but has the NF-Y binding element. In a protoplast test system ARR1-SRDX suppressed ARR6:GUS reporter gene activation by different B-type ARRs. Moreover, induction of SOC1 by ABA was hampered in abf3 abf4 mutants. We identified SOC1 as a direct downstream target of ABF3/4, and found that SOC1 mRNA levels were lower in abf3 abf4 than in wild-type plants. Ectopic expression of ABF3 or ABF4 in the vasculature, but not in the shoot apex, induced early flowering, whereas expression of ABF3 fused with the SRDX transcriptional repressor domain delayed flowering. The abf3 abf4 mutant displayed ABA-insensitive late flowering under long-day conditions. Here, we show that Arabidopsis thaliana ABF3 and ABF4 regulate flowering in response to drought through transcriptional regulation of the floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 ( SOC1). Abscisic acid (ABA) mediates plant responses to drought, but the role of ABA-responsive element (ABRE)-binding factors (ABFs) in the drought-escape response is poorly understood. The publisher has kindly granted permission to reproduce this abstract on TAIR. This study demonstrates the usefulness of CRES-T to overcome redundancy in transcription factor families for functional studies. In addition, a role for B-type ARRs in mediating crosstalk with other pathways is supported by resistance of 35S:ARR1-SRDX seeds to phyB-mediated inhibition of germination by far-red light. Collectively, the suppression of pleiotropic cytokinin activities by a dominant repressor version of a B-type ARR indicates that this protein family is involved in mediating most, if not all, of the cytokinin activities in Arabidopsis. The transcript levels of more than 500 genes were >2.5-fold reduced in 35S:ARR1-SRDX transgenic seedlings suggesting a broad function of B-type ARRs. The rapid induction of a large part of cytokinin response genes was dampened. Several bioassays showed that 35S:ARR1-SRDX plants have an increased resistance towards cytokinin. In a protoplast test system ARR1-SRDX suppressed ARR6:GUS reporter gene activation by different B-type ARRs. We generated a dominant repressor version of Arabidopsis response regulator ARR1 (ARR1-SRDX) using chimeric repressor silencing technology (CRES-T) in order to study the extent of the contribution of B-type response regulators to cytokinin activities. In planta functional analysis of this family is hampered by the high level of functional redundancy of its eleven members. ![]() One component of this system are B-type response regulators, transcription factors mediating at least part of the response to cytokinin. The signal transduction of the phytohormone cytokinin is mediated by a multi-step His-to-Asp phosphorelay system. Abstract: Transcription factors (TFs) fused to the SRDX (a modified repressor domain at the C-terminal region of Arabidopsis SUPERMAN (SUPRD) with the sequence. Heyl, Alexander, Ramireddy, Eswar, Brenner, Wolfram G, Riefler, Michael, Allemeersch, Joke, Schmulling, Thomas Title: The Transcriptional Repressor ARR1-SRDX Suppresses Pleiotropic Cytokinin Activities in Arabidopsis.
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