Buried seedlings undergo dramatic developmental transitions when they emerge from soil into sunlight. As central transcription factors suppressing light responses, PHYTOCHROME-INTERACTING FACTORs (PIFs) and ETHYLENE-INSENSITIVE 3 (EIN3) actively function in darkness and must be promptly repressed upon light to initiate deetiolation. Microproteins are evolutionarily conserved small single-domain proteins that act as posttranslational regulators in eukaryotes. Although hundreds to thousands of microproteins are predicted to exist in plants, their target molecules, biological roles, and mechanisms of action remain largely unknown. Here, we show that two microproteins, miP1a and miP1b (miP1a/b), are robustly stimulated in the dark-to-light transition. miP1a/b are primarily expressed in cotyledons and hypocotyl, exhibiting tissue-specific patterns similar to those of PIFs and EIN3. We demonstrate that PIFs and EIN3 assemble functional oligomers by self-interaction, while miP1a/b directly interact with and disrupt the oligomerization of PIFs and EIN3 by forming nonfunctional protein complexes. As a result, the DNA binding capacity and transcriptional activity of PIFs and EIN3 are predominantly suppressed. These biochemical findings are further supported by genetic evidence. miP1a/b positively regulate photomorphogenic development, and constitutively expressing miP1a/b rescues the delayed apical hook unfolding and cotyledon development of plants overexpressing PIFs and EIN3. Our study reveals that microproteins provide a temporal and negative control of the master transcription factors' oligomerization to achieve timely developmental transitions upon environmental changes.

当埋入的幼苗从土壤进入阳光时，它们会经历剧烈的发育过渡。由于中枢转录因子抑制光反应，因此植物色素相互作用因子（PIF）和乙烯不敏感3（EIN3）在黑暗中活跃发挥作用，必须在光下迅速抑制，以启动脱脂作用。微蛋白是进化保守的小单结构域蛋白，在真核生物中充当翻译后调节剂。尽管预计植物中会存在成百上千种微蛋白，但它们的靶分子，生物学作用和作用机理仍然未知。在这里，我们显示了两种微蛋白，miP1a和miP1b（miP1a / b），在从暗到光的过渡过程中受到强烈刺激。miP1a / b它们主要在子叶和下胚轴中表达，表现出与PIF和EIN3相似的组织特异性模式。我们证明，PIF和EIN3通过自我相互作用组装功能性低聚物，而miP1a / b直接与PIF和EIN3相互作用并通过形成非功能性蛋白复合物破坏寡聚化。结果，PIF和EIN3的DNA结合能力和转录活性被显着抑制。这些生化发现得到遗传证据的进一步支持。miP1a / b积极调节光形态发生的发展，并组成型表达miP1a / b可以挽救过表达PIF的植物的延迟的根尖钩展开和子叶发育和EIN3。我们的研究表明，微蛋白可以暂时控制主转录因子的寡聚，从而在环境变化时及时实现发育过渡。