MYB transcription factors are involved in many biological processes, including metabolism, development and responses to biotic and abiotic stresses. RADIALIS-LIKE SANT/MYB 1 (RSM1) belongs to a MYB-related subfamily, and previous transcriptome analysis suggests that RSM1 may play roles in plant development, stress responses and plant hormone signaling. However, the molecular mechanisms of RSM1 action in response to abiotic stresses remain obscure. We show that down-regulation or up-regulation of RSM1 expression alters the sensitivity of seed germination and cotyledon greening to abscisic acid (ABA), NaCl and mannitol in Arabidopsis. The expression of RSM1 is dynamically regulated by ABA and NaCl. Transcription factors ELONGATED HYPOCOTYL 5 (HY5) and HY5 HOMOLOG (HYH) regulate RSM1 expression via binding to the RSM1 promoter. Genetic analyses reveal that RSM1 mediates multiple functions of HY5 in responses of seed germination, post-germination development to ABA and abiotic stresses, and seedling tolerance to salinity. Pull-down and BiFC assays show that RSM1 interacts with HY5/HYH in vitro and in vivo. RSM1 and HY5/HYH may function as a regulatory module in responses to ABA and abiotic stresses. RSM1 binds to the promoter of ABA INSENSITIVE 5 (ABI5), thereby regulating its expression, while RSM1 interaction also stimulates HY5 binding to the ABI5 promoter. However, no evidence was found in the dual-luciferase transient expression assay to support that RSM enhances the activation of ABI5 expression by HY. In summary, HY5/HYH and RSM1 may converge on the ABI5 promoter and independently or somehow dependently regulate ABI5 expression and ABI5-downstream ABA and abiotic stress-responsive genes, thereby improving the adaption of plants to the environment.

MYB转录因子参与许多生物过程，包括代谢，发育以及对生物和非生物胁迫的反应。RADIALIS-like SANT / MYB 1（RSM1）属于与MYB相关的亚科，以前的转录组分析表明RSM1可能在植物发育，胁迫反应和植物激素信号传导中发挥作用。但是，RSM1响应非生物胁迫的分子机制仍然不清楚。我们表明，RSM1表达的下调或上调改变了种子萌发和子叶绿化对拟南芥中脱落酸（ABA），NaCl和甘露醇的敏感性。RSM1的表达由ABA和NaCl动态调节。转录因子长双羟基5（HY5）和HY5同源（HYH）通过与RSM1启动子结合来调节RSM1表达。遗传分析表明，RSM1介导HY5的多种功能，包括种子萌发，发芽后对ABA和非生物胁迫的发育以及幼苗对盐分的耐受性。下拉和BiFC分析表明，RSM1在体外和体内均与HY5 / HYH相互作用。RSM1和HY5 / HYH可能对ABA和非生物胁迫起调节模块的作用。RSM1与ABA INSENSITIVE 5（ABI5），从而调节其表达，而RSM1相互作用也刺激HY5与ABI5启动子的结合。但是，在双荧光素酶瞬时表达试验中未发现任何证据支持RSM增强HY对ABI5表达的激活。总之，HY5 / HYH和RSM1可能会收敛于ABI5启动子，并独立或以某种方式依赖性地调节ABI5表达和ABI5下游ABA和非生物胁迫响应基因，从而改善植物对环境的适应性。