The ATAF2 Transcription Factor, Brassinosteroid Catabolism and Plant Development

非技术解释：植物通过光合作用将阳光作为能量来源。植物还利用环境中的光线作为信息来源，以优化生长和发育。植物利用这些信息的一种方式是调节被称为油菜素类固醇的促生长激素的水平。油菜素类固醇在包括农作物在内的植物生长中起着重要作用。该项目将研究一种名为ATAF2的蛋白质如何通过改变油菜素类固醇水平来调节植物生长，以应对光环境的变化。该项目的发现可能有助于确定作物在苗期生长、成虫生物量、开花时间、产量和对环境胁迫的反应等过程中的改良目标。技术描述：油菜素类固醇激素调节的一个重要方面是油菜素类固醇失活，由包括P450s、BAS1/CYP734A1和SOB7/CYP72C1在内的酶催化。这些酶的转录调控对于它们在调节幼苗和成体植物发育中的作用是重要的。NAC家族转录因子ATAF2是BAS1和SOB7的转录抑制因子。ATAF2与BAS1和SOB7启动子结合。功能丧失和功能获得的ATAF2突变苗具有相反的油菜素类固醇反应表型。遗传分析还表明，ATAF2以一种依赖于光通量速率的方式调控光响应的下胚轴生长。此外，ATAF2的转录积累受光的抑制。这些结果表明，ATAF2可能与其他家族成员一起，作为油菜素类固醇分解代谢和光介导的拟南芥幼苗发育的新的整合子。本项目将验证以下假设：1)ATAF2整合了与幼苗发育相关的多条途径：除了参与油菜素类固醇和光介导的发育外，ATAF2还参与生长素的生物合成和抗病。本项目将进一步剖析ATAF2调控幼苗生长发育的分子网络。2)ATAF2的活性是一个动态的过程：初步结果表明，ATAF2与BAS1和SOB7启动子结合，ATAF2的遗传状态影响这些油菜素类固醇失活基因的转录积累。本项目将研究ATAF2与这些启动子结合的动态过程，以及通过改变光或油菜素类固醇水平来调节ATAF2的作用。该项目还将研究调节ATAF2表达的潜在转录因子。3)ATAF2和近亲有重叠的功能：初步结果表明，与ATAF2密切相关的NAC转录因子也调节幼苗的生长，对油菜素类固醇和变化的光条件做出反应。该项目将研究ATAF2与其近亲ANAC102和ATAF1之间潜在的功能冗余。4)油菜素类固醇失活对植物发育很重要：在拟南芥中已鉴定出至少8种油菜素类固醇失活酶，它们通过至少5种不同的生化作用发挥作用。这个项目将使用基因编辑来研究这个“生化过程”酶家族不同成员之间的遗传相互作用。

Nontechnical Explanation: Plants use sunlight as a source of energy through the process of photosynthesis. Plants also use the light in their environment as a source of information to optimize growth and development. One way plants use this information is to regulate the levels of the growth-promoting hormones called brassinosteroids. Brassinosteroids play an important role in the growth of plants including crops. This project will study how a protein called ATAF2 regulates plant growth by altering brassinosteroid levels in response to changes in the light environment. Findings from this project may help identify targets for crop improvement with regard to processes such as seedling growth, adult biomass, flowering time, yield and responses to environmental stress.Technical Description: An important aspect of brassinosteroid hormone regulation is brassinosteroid-inactivation, catalyzed by enzymes including the P450s, BAS1/CYP734A1 and SOB7/CYP72C1. Transcriptional regulation of these enzymes is important for their role in modulating seedling and adult plant development. A NAC-family transcription factor, ATAF2, has been identified as a transcriptional repressor of both BAS1 and SOB7. ATAF2 binds the promoters of BAS1 and SOB7. Loss- and gain-of-function ATAF2 mutant seedlings have opposite brassinosteroid-response phenotypes. Genetic analysis also demonstrates that ATAF2 modulates light-responsive hypocotyl growth in a fluence-rate-dependent manner. In addition, transcript accumulation of ATAF2 is repressed by light. These results indicate that ATAF2, possibly in concert with other family members, acts as a novel integrator of brassinosteroid catabolism and light-mediated seedling development in Arabidopsis. The following hypotheses will be tested in this project: 1) ATAF2 integrates multiple pathways associated with seedling development: In addition to ATAF2's involvement in brassinosteroid- and light-mediated development, ATAF2 has been implicated in auxin biosynthesis and disease resistance. This project will further dissect the molecular networks of ATAF2-regulated seedling growth and development. 2) ATAF2 activity is a dynamic process: Preliminary results demonstrate that ATAF2 binds to the BAS1 and SOB7 promoters and that the genetic state of ATAF2 affects the transcript accumulation of these brassinosteroid-inactivating genes. This project will examine the dynamic process of ATAF2 binding to these promoters and its regulation by changing light or brassinosteroid levels. This project will also examine potential transcription factors that regulate ATAF2 expression. 3) ATAF2 and close relatives have overlapping functions: Preliminary results demonstrate that closely related NAC transcription factors also regulate seedling growth in response to both brassinosteroids and changing light conditions. This project will examine potential functional redundancy between ATAF2 and its close relatives, ANAC102 and ATAF1. 4) Brassinosteroid inactivation is important for plant development: At least eight brassinosteroid-inactivating enzymes have been identified in Arabidopsis, which function via at least five different biochemistries. This project will use gene editing to study genetic interactions between different members of this "biochemical process" enzyme family.