Abstract：
Combinatorial interactions between different regulators diversify and enrich the chance of transcriptional regulation in eukaryotic cells. However, a dose-dependent functional switch of homologous transcriptional repressors has rarely been reported. Here, we show that SHY2, an auxin/indole-3-acetic acid (Aux/IAA) repressor, exhibits a dose-dependent bimodal role in auxin-sensitive root-hair growth and gene transcription in Arabidopsis, whereas other Aux/IAA homologs consistently repress the auxin responses. The co-repressor (TOPLESS [TPL])-binding affinity of a bimodal Aux/IAA was lower than that of a consistently repressing Aux/IAA. The switch of a single amino acid residue in the TPL-binding motif between the bimodal form and the consistently repressing form switched their TPL-binding affinity and transcriptional and biological roles in auxin responses. Based on these data, we propose a model whereby competition between homologous repressors with different co-repressor-binding affinities could generate a bimodal output at the transcriptional and developmental levels.
摘要：
不同调节因子之间的组合相互作用使真核细胞中转录调控的机会多样化并丰富。然而,同源转录抑制因子的剂量依赖性功能开关很少有报道。这里,我们显示SHY2，生长素/吲哚-3-乙酸（Aux/IAA）阻遏物，在拟南芥的生长素敏感的根毛生长和基因转录中表现出剂量依赖性的双峰作用，而其他Aux/IAA同源物始终抑制生长素反应。双峰Aux/IAA的共阻遏物（TOPLESS[TPL]）结合亲和力低于一致抑制的Aux/IAA。TPL结合基序中的单个氨基酸残基在双峰形式和一致抑制形式之间的转换改变了它们的TPL结合亲和力以及在生长素反应中的转录和生物学作用。基于这些数据,我们提出了一个模型，通过该模型，具有不同共抑制子结合亲和力的同源抑制子之间的竞争可以在转录和发育水平上产生双峰输出。
