近期，中国农业大学李继刚课题组在Molecular plant 发表了题为PHYTOCHROME-INTERACTING FACTORS Interact with the ABA Receptors PYL8 and PYL9 to Orchestrate ABA Signaling in Darkness 的研究论文，该论文揭示转录因子PHYTOCHROME-INTERACTING FACTORS (PIFs) 通过直接结合ABI5基因的启动子并且激活ABI5的表达，在黑暗下特异调控植物的ABA信号途径。此外，文章还发现ABA受体PYL8/PYL9能够和PIFs直接相互作用，并且介导PIFs对ABI5的转录调控。

PIFs 是一类与光受体（包括光敏色素和隐花色素）发生物理相互作用的basic helix-loop-helix (bHLH) 转录因子。以往的研究表明，PIFs在黑暗中积累，抑制了幼苗的光形态建成，并通过不同的感光系统和激素途径来调控植物的生长发育。在本研究中，作者发现PIFs在苗期对ABA信号通路有正调控作用，特别是在黑暗中。作者发现在外源ABA处理条件下，PIFs通过直接与ABI5启动子中的G-box基序结合，在黑暗中对的ABI5转录和蛋白水平起到了正调控作用。与此相一致，PIFs和ABI5 启动子中的G-box基序决定了ABI5在黑暗中的表达，而ABI5的过表达可以挽救pifq突变体(即pif1, pif3, pif4和pif5的四突变体)在黑暗中对ABA不敏感的表型。此外，作者还发现PIFs可以与ABA受体PYL8和PYL9发生物理性的相互作用，而这种相互作用不受ABA的调节。进一步分析表明，PYL8和PYL9在黑暗中促进了PIF4蛋白的积累，增强了PIF4与ABI5启动子的结合，但对PIF4介导的ABI5激活具有负调控作用。

综上所述，这些结果表明，PIFs与ABA受体相互作用，通过控制ABI5的表达在黑暗中协调ABA信号的传递，这为PIFs作为信号整合因子在调节植物生长发育中的关键作用提供了新的见解。

在黑暗下，PIFs调控植物ABA信号途径的工作模式图。PIFs直接结合在ABI5基因的启动子上并且激活其表达，而ABA受体PYL8和PYL9与PIFs相互作用，介导PIFs对ABI5的转录调控。

附：

ABSTRACT

PHYTOCHROME-INTERACTING FACTORS (PIFs) are a group of basic helix-loop-helix transcription factors that can physically interact with photoreceptors, including phytochromes and cryptochromes. It was previously demonstrated that PIFs accumulated in darkness and repressed seedling photomorphogenesis, and that PIFs linked different photosensory and hormonal pathways to control plant growth and development. In this study, we show that PIFs positively regulate the ABA signaling pathway during the seedling stage specifically in darkness. We found that PIFs positively regulate ABI5 transcript and protein levels in darkness in response to exogenous ABA treatment by binding directly to the G-box motifs in the ABI5 promoter. Consistently, PIFs and the G-box motifs in the ABI5 promoter determine ABI5 expression in darkness, and overexpression of ABI5 could rescue the ABA-insensitive phenotypes of pifq mutants in the dark. Moreover, we discovered that PIFs can physically interact with the ABA receptors PYL8 and PYL9, and that this interaction is not regulated by ABA. Further analyses showed that PYL8 and PYL9 promote PIF4 protein accumulation in the dark and enhance PIF4 binding to the ABI5 promoter, but negatively regulate PIF4-mediated ABI5 activation. Taken together, our data demonstrate that PIFs interact with ABA receptors to orchestrate ABA signaling in darkness by controlling ABI5 expression, providing new insights into the pivotal roles of PIFs as signal integrators in regulating plant growth and development.

文章链接：

https://doi.org/10.1016/j.molp.2020.02.001