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.

植物色素相互作用因子（PIF）是一组基本的螺旋-环-螺旋转录因子，可以与光感受器（包括植物色素和隐色色素）进行物理相互作用。先前已证明PIF在黑暗中积累并抑制了幼苗的光形态发生，并且PIF链接了不同的光敏和激素途径来控制植物的生长和发育。在这项研究中，我们表明PIF积极调节ABA信号转导通路特别是在黑暗中的苗期。我们发现PIF通过直接与ABI5启动子中的G-box基序结合，在黑暗中积极调节ABI5转录本和蛋白质水平，以响应外源ABA处理。一致地，ABI5中的PIF和G-box图案启动子决定了ABI5在黑暗中的表达，而ABI5的过表达可以在黑暗中挽救pifq突变体的ABA不敏感表型。此外，我们发现PIF可以与ABA受体PYL8和PYL9发生物理相互作用，并且这种相互作用不受ABA的调控。进一步的分析表明，PYL8和PYL9可以促进PIF4蛋白在黑暗中的积累，并增强PIF4与ABI5启动子的结合，但会对PIF4介导的ABI5激活产生负调控。综上所述，我们的数据表明，PIF与ABA受体相互作用，通过控制ABI5在黑暗中协调ABA信号传导。 表达，为PIF在调节植物生长和发育中作为信号整合剂的关键作用提供了新见解。