Regulation of seedling de-etiolation by light

拟南芥的光敏色素(PHY)感光受体家族由五个成员组成(PhyA到PhyE)，它们控制着对环境光环境的许多发育反应。在光敏和生化功能的表征以及信号中间体的鉴定和功能表征方面已经取得了重大进展。然而，PHY信号的生化机制仍不清楚。为了研究早期PHY信号事件，已分离和鉴定了PHY相互作用因子，如PIF1。PIF1是一种碱性螺旋-环-螺旋(BHLH)转录因子，它与具有生物活性的PhyA和PhyB以及另一种bHLH因子PIF3相互作用。PIF1与一个G-box(CACGTG)DNA序列基序结合，在许多光调控启动子中常见。PIF1还被证明在瞬时实验中激活了转录，远红光和红光分别以PhyA和PhyB依赖的方式下调了转录激活活性。Pif1过表达和pif1 T-DNA插入突变体表现出幼苗脱黄化缺陷，包括异常的下胚轴伸长和发育调节的绿色化丧失。这些结果表明，PIF1是PHY介导的幼苗去黄化过程的关键调控因子。这项拟议的研究将利用分子遗传学、生化和功能基因组学方法来研究PIF1控制幼苗脱黄化的分子机制。具体地说，将对PIF1靶基因进行鉴定和功能鉴定，并将研究PIF1的分子功能，以检验它是作为天然靶基因启动子的转录激活因子还是转录抑制因子。此外，还将在体内研究PIF1-PHY和PIF1-PIF3之间的物理相互作用的生物学意义。由于PIF1是一个主要的PHY信号伙伴，其活性受PHY调控，本研究的结果将为PHY信号的机制提供基础信息。预期的更广泛的影响：光被认为是控制植物生长和发育的最重要的环境因素之一，包括许多重要的农艺性状，如种子萌发、幼苗的建立和存活、株高、叶面积、开花时间和种植密度。了解光调控植物生长发育的机理，将为农业生物技术利用减少化肥提高作物产量提供极好的工具。这一建议也非常适合培养下一代科学家，包括本科生、研究生和博士后。他们在光信号方面的培训将给他们一个独特的机会，为光生物学和生物技术领域做出重大贡献。

PROJECT SUMMARYIntellectual Merits: The phytochrome (phy) family of sensory photoreceptors in Arabidopsis consists of five members (phyA to phyE) that control many developmental responses to the ambient light environment. Significant progress has been made on characterization of photosensory and biochemical functions and in the identification and functional characterization of signaling intermediates. However, the biochemical mechanism of phy signaling is still not clear. To examine early phy signaling events, phy interacting factors such as PIF1 have been isolated and characterized. PIF1 is a basic helix-loop-helix (bHLH) transcription factor that interacts strongly with the biologically active form of phyA and phyB, as well as another bHLH factor, PIF3. PIF1 binds to a G-box (CACGTG) DNA sequence motif commonly found in many light regulated promoters. PIF1 has also been shown to activate transcription in a transient assay, and the transcriptional activation activity was downregulated by far-red and red light in a phyA- and phyB-dependent manner, respectively. PIF1 overexpressors and pif1 T-DNA insertional mutants showed defective seedling de-etiolation, including aberrant hypocotyl elongation and developmentally regulated loss of greening. These results suggest that PIF1 is a key regulator of the phy-mediated control of the seedling de-etiolation process. The proposed study will investigate the molecular mechanism by which PIF1 controls seedling de-etiolation using molecular genetic, biochemical and functional genomic approaches. Specifically, the PIF1 target genes will be identified and functionally characterized, and the molecular function of PIF1 will be investigated to examine whether it acts as a transcriptional activator or repressor from a native target gene promoter. In addition, the biological significance of physical interactions between PIF1-phy and PIF1-PIF3 will be investigated in vivo. Since PIF1 is a primary phy-signaling partner whose activity is regulated by phy, the results from this study will provide fundamental information on the mechanism of phy signaling.Expected Broader Impacts: Light is arguably one of the most important environmental factors controlling plant growth and development, including many agronomically important traits such as seed germination, seedling establishment and survival, plant height, leaf area, flowering time and plantation density. Understanding the mechanism of light-regulated plant growth and development will provide excellent tools to apply in agricultural biotechnology for increased crop production using reduced amount of fertilizers. This proposal is also ideally suited for training of the next generation of scientists, including undergraduate, graduate and postdoctoral students. Their training in light signaling will give them a unique opportunity to make significant contributions to the field of photobiology and biotechnology.