Graduate School of Integrated Sciences for Life, Hiroshima University, Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
Plant Mol Biol. 2021 Mar;105(4-5):463-482. doi: 10.1007/s11103-020-01101-z. Epub 2021 Jan 21.
SCL3 inhibits transcriptional activity of IDD-DELLA complex by acting as a co-repressor and repression activity is enhanced in the presence of GAF1 in a TOPLESS-independent manner. GRAS [GIBBERELLIN-INSENSITIVE (GAI), REPRESSOR OF ga1-3 (RGA) and SCARECROW (SCR)] proteins are a family of plant-specific transcriptional regulators that play diverse roles in development and signaling. GRAS family DELLA proteins act as growth repressors by inhibiting gibberellin (GA) signaling in response to developmental and environmental cues. DELLAs also act as co-activators of transcription factor GAI-ASSOCIATED FACTOR1 (GAF1)/INDETERMINATE DOMAIN2 (IDD2), the GAF1-DELLA complex activating transcription of GAF1 target genes. GAF1 also interacts with TOPLESS (TPL), a transcriptional co-repressor, in the absence of DELLA, the GAF1-TPL complex repressing transcription of the target genes. SCARECROW-LIKE3 (SCL3), another member of the GRAS family, is thought to inhibit transcriptional activity of the IDD-DELLA complex through competitive interaction with IDD. Here, we also revealed that SCL3 inhibits transcriptional activation by the GAF1-DELLA complex via repression activity rather than via competitive inhibition of the GAF1-DELLA interaction. Moreover, the repression activity of SCL3 was enhanced by GAF1 in a TPL-independent manner. While the GRAS domain of DELLA has transcriptional activation activity, that of SCL3 has repression activity. SCL3 also inhibited transcriptional activity of GAF1-RGA fusion proteins. Results from the co-immunoprecipitation assays and the yeast three-hybrid assay suggested the possibility that SCL3 forms a ternary complex with GAF1 and DELLA. These findings provide important information on DELLA-regulated GA signaling and new insight into the transcriptional repression mechanism.
SCL3 通过作为共抑制子来抑制 IDD-DELLA 复合物的转录活性，并且在 TOPLESS 非依赖性方式下，在存在 GAF1 的情况下抑制活性得到增强。GRAS [赤霉素不敏感（GAI），ga1-3 的抑制物（RGA）和 SCARECROW（SCR）]蛋白是一类植物特异性转录调节剂，在发育和信号转导中发挥多种作用。GRAS 家族的 DELLA 蛋白通过响应发育和环境线索抑制赤霉素（GA）信号来作为生长抑制剂。DELLAs 还作为转录因子 GAI-ASSOCIATED FACTOR1（GAF1）/不确定域 2（IDD2）的共激活因子起作用，GAF1-DELLA 复合物激活 GAF1 靶基因的转录。GAF1 还在没有 DELLA 的情况下与 TOPLESS（TPL）相互作用，TPL 是一种转录共抑制子，GAF1-TPL 复合物抑制靶基因的转录。SCARECROW-LIKE3（SCL3），GRAS 家族的另一个成员，被认为通过与 IDD 的竞争相互作用抑制 IDD-DELLA 复合物的转录活性。在这里，我们还揭示了 SCL3 通过抑制活性而不是通过竞争性抑制 GAF1-DELLA 相互作用来抑制 GAF1-DELLA 复合物的转录激活。此外，SCL3 的抑制活性在 TPL 非依赖性方式下被 GAF1 增强。虽然 DELLA 的 GRAS 结构域具有转录激活活性，但 SCL3 的 GRAS 结构域具有抑制活性。SCL3 还抑制 GAF1-RGA 融合蛋白的转录活性。共免疫沉淀测定和酵母三杂交测定的结果表明，SCL3 与 GAF1 和 DELLA 形成三元复合物的可能性。这些发现提供了有关 DELLA 调节的 GA 信号转导的重要信息，并为转录抑制机制提供了新的见解。
