Dual role of the transcription factor PHR1 in Lotus japonicus, a model plant for root symbioses

本研究的目的是表征模式豆科植物荷花（Lotus japonicus）中磷酸盐（Pi）饥饿反应和丛枝菌根（AM）共生的共同分子机制。AM共生有利于低Pi有效度生境植物的Pi获取。相反，高Pi条件抑制了功能性菌根的发育。潜在的分子机制在很大程度上是未知的。本文将研究转录因子PHR1在调节Pi饥饿诱导（PSI）基因和共生体形成中的双重作用，共生体是营养物质和代谢物双向交换的场所。首先，我们将在PHR1突变体和过表达PHR1的植物中研究PHR1依赖性和非依赖性PSI基因的鉴定。接下来，我们将研究am诱导型/高pi抑制型菌根基因表达的共性以及PSI基因调控的抑制/抑制机制。第二个项目将研究PHR1依赖性生理反应和am特异性基因的调控，而第三个项目将重点研究顺式调控模块及其对PHR1活性的依赖性。该模块由P1BS和CTTC两个基序组成，旨在整合am特异性和Pi抑制转运体基因调控。这项工作将有助于阐明协调调节AM共生体发育以响应Pi有效性的调控网络。

The objective of this proposal is to characterize the common molecular mechanisms underlying both the phosphate (Pi) starvation response and the arbuscular mycorrhizal (AM) symbiosis in the model legume Lotus japonicus. AM symbiosis facilitates Pi acquisition in plants in habitats of low Pi availability. In contrast, high Pi conditions suppress the development of a functional mycorrhiza. The underlying molecular mechanisms are largely unknown. Here a dual role of transcription factor PHR1 in the regulation of Pi starvation inducible (PSI) genes and the formation of the symbiosome, which is the site of bi-directional exchange of nutrients and metabolites, will be investigated. Firstly, the identification of PHR1- dependent and -independent PSI genes will be studied in phr1 mutants and in plants overexpressing PHR1. Next commonalities between AM-inducible/high Pi-repressible mycorrhizal gene expression and the repression/derepression mechanism underlying PSI gene regulation will be studied. While in the second project PHR1-dependent physiological responses and the regulation of AM-specific genes will be investigated, the third project will focus on a cis-acting regulatory module and its dependence on PHR1 activity. This module consists of two motifs, P1BS and CTTC, and is proposed to integrate AM-specific and Pi repressible transporter gene regulation. This work will help to elucidate the regulatory network which coordinately regulates AM symbiosome development in response to Pi availability.