The opening of the embryonic leaves (cotyledons) as seedlings emerge from the dark soil into the light is crucial to ensure the survival of the plant. Seedlings that sprout in the dark elongate rapidly to reach light but keep their cotyledons closed. During de-etiolation, the transition from dark to light growth, elongation slows and the cotyledons open. Here, we report that the transcription factor ACTIVATING FACTOR1 (ATAF1) participates in de-etiolation and facilitates light-induced cotyledon opening. The transition from dark to light rapidly induced ATAF1 expression and ATAF1 accumulation in cotyledons. Seedlings lacking or overexpressing ATAF1 exhibited reduced or enhanced cotyledon opening, respectively, and transcriptomic analysis indicated that ATAF1 repressed the expression of genes associated with growth and cotyledon closure. The activation of the photoreceptor phytochrome A (phyA) by far-red light induced its association with the ATAF1 promoter and stimulation of ATAF1 expression. The transcription factor ELONGATED HYPOCOTYL5 (HY5), which is also activated in response far-red light, cooperated with phyA to induce ATAF1 expression. ATAF1 and HY5 interacted with one another and cooperatively repressed the expression of growth-promoting and cotyledon closure genes. Together, our study reveals a mechanism through which far-red light promotes cotyledon opening.

中文翻译：

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ATAF1和HY5的协同转录调控促进拟南芥光诱导子叶开放

当幼苗从黑暗的土壤中出现到阳光下时，胚叶（子叶）的张开对于确保植物的生存至关重要。在黑暗中发芽的幼苗会迅速伸长以达到光照，但子叶保持闭合。在去黄化过程中，从黑暗生长过渡到光照生长，伸长减慢，子叶张开。在这里，我们报道转录因子激活因子1（ATAF1）参与去黄化并促进光诱导子叶打开。快速诱导从黑暗到光明的转变ATAF1子叶中的表达和 ATAF1 积累。缺乏或过度表达 ATAF1 的幼苗分别表现出子叶开放减少或增强，转录组分析表明 ATAF1 抑制与生长和子叶闭合相关的基因的表达。远红光激活光感受器光敏色素 A (phyA)，诱导其与ATAF1促进剂和刺激ATAF1表达。转录因子 ELONGATED HYPOCOTYL5 (HY5) 也能响应远红光而被激活，与 phyA 合作诱导ATAF1表达。ATAF1 和 HY5 相互作用，共同抑制生长促进基因和子叶闭合基因的表达。总之，我们的研究揭示了远红光促进子叶开放的机制。