Phytohormone signaling in arbuscular mycorrhiza development

丛枝菌根（AM）是一种广泛存在的植物与球囊菌门真菌的共生体，其基于共生体之间的营养交换：植物受益于增加的矿物营养吸收，而活体营养真菌则获得光合固定碳。AM真菌在植物根部的定殖涉及通过可扩散的信号分子的相互识别，随后菌丝对接到根表面，穿透外细胞层，并在皮层细胞内形成分支丛枝。细胞内定植是由一个进化古老的信号转导程序称为共同SYM途径。植物还通过未知的机制动态地控制定殖的程度，以根据环境条件及其产生的生理状态来优化共生相互作用。最近的报道强调了植物激素，植物发育的调节剂，在控制AM定殖的突出作用。然而，这方面的知识仍然是初步的和机械的方法，需要解开AM和整个植物发育之间的明显的相互联系的分子基础。本研究旨在探讨植物激素信号在AM发育中的作用机制和结果。它建立在我以前的发现，karrikin受体复合物的两个组成部分，α/β-折叠水解酶D14 L和F-box蛋白MAX2，是必不可少的根由AM真菌的殖民。Karrikins是新描述的从烟雾中分离出来的丁烯内酯，最初发现在火灾后的环境中引发植物发芽。它们还显示出独立于火萌发的植物中的激素活性，并且D14 L和karrikin响应性的广泛系统发育分布表明植物产生内源性karrikin样物质。我的惊人发现是，karrikin-receptor模块参与了植物与共生真菌的日常相互作用，这表明它比以前假设的更广泛地参与调节植物生命。我的目标是1。阐明D14 L MAX2模块在AM发育过程中的动力学、感知和信号转导机制; 2.阐明D14 L信号传导特异性是如何确定的; 3.鉴定AM发育所需的D14 L MAX2信号传导的下游靶标; 4.揭示D14 L MAX2模块与其他植物激素信号通路的相互作用。拟议的研究将结合联合收割机反向遗传学，生理和AM检测，转录组学，蛋白质相互作用的研究，并通过荧光实时成像的D14 L MAX2信号组件和下游目标在AM发展的时空定位。它将使用已经建立的根系共生模式植物百脉根。我希望这项工作不仅将揭示通过激素信号控制AM共生的机制，而且将有助于对AM领域以外的植物发育中激素功能的一般理解。

Arbuscular mycorrhiza (AM) is a widespread symbiosis of plants with fungi of the Glomeromycota that is based on the exchange of nutrients between the symbionts: The plant benefits from increased mineral nutrient uptake while the biotrophic fungus receives photosynthetically fixed carbon. Colonization of plant roots by AM fungi involves mutual recognition through diffusible signal molecules, followed by hyphal docking to the root surface, penetration of the outer cell layers, and formation of branched arbuscules inside cortex cells. Intracellular colonization is steered by an evolutionary ancient signal transduction program called common SYM pathway. The plant also dynamically controls the extent of colonization through unknown mechanisms to optimize the symbiotic interaction according to environmental conditions and its resulting physiological state. Recent reports highlight a prominent role of phytohormones, regulators of plant development, in the control of AM colonization. However, this knowledge is still rudimentary and mechanistic approaches are needed to unravel the molecular basis for the obvious interconnections between AM and whole plant development. This proposal is designed to study mechanisms and outcomes of plant hormone signaling in AM development. It builds on my previous discovery that two components of the karrikin receptor complex, the alpha/beta-fold hydrolase D14L and the F-box protein MAX2, are essential for the colonization of roots by AM fungi. Karrikins are newly described butenolides isolated from smoke and originally found to trigger plant germination in post-fire environments. They also display hormonal activity in plants that germinate independently of fire and the wide phylogenetic distribution of D14L and karrikin-responsiveness suggests that plants produce an endogenous karrikin-like substance. My surprising finding that the karrikin-receptor module is involved in the everyday interaction of plants with symbiotic fungi shows that it is more broadly implicated in regulating plant life than previously assumed. Here I aim to 1. elucidate the dynamics, perception and signaling mechanisms of the D14L MAX2 module during AM development; 2. unravel how D14L signaling specificity is determined; 3. identify downstream targets of D14L MAX2 signaling required for AM development; 4. uncover interactions of the D14L MAX2 module with other phytohormone signaling pathways. The proposed research will combine reverse genetics, physiological and AM assays, transcriptomics, protein interaction studies, and spatiotemporal localization by fluorescence live imaging of D14L MAX2 signaling components and downstream targets during AM development. It will use the well-established root symbiosis model plant Lotus japonicus. I expect that this work not only will reveal mechanisms that control AM symbiosis via hormone signaling but will contribute to the general understanding of hormone function in plant development beyond the AM field.