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

该建议的目的是表征模式豆科植物百脉根中磷酸盐（Pi）饥饿反应和丛枝菌根（AM）共生的共同分子机制。AM共生促进了低磷生境中植物对磷的吸收。相反，高Pi条件抑制功能性菌根的发育。潜在的分子机制在很大程度上是未知的。在这里的双重作用的转录因子PHR 1在Pi饥饿诱导（PSI）基因的调节和形成的共生体，这是双向交换的营养物质和代谢产物的网站，将进行调查。首先，将在phr 1突变体和过表达PHR 1的植物中研究PHR 1依赖性和非依赖性PSI基因的鉴定。接下来将研究AM诱导/高Pi抑制的菌根基因表达和PSI基因调控的抑制/去抑制机制之间的共性。在第二个项目中，将研究PHR 1依赖的生理反应和AM特异性基因的调控，而第三个项目将重点关注顺式作用调控模块及其对PHR 1活性的依赖性。该模块由两个基序组成，P1 BS和CTTC，并建议整合AM特异性和Pi抑制性转运蛋白基因调控。这项工作将有助于阐明协调调节AM共生体发育的调控网络，以响应Pi的可用性。

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.