Molecular mechanism for the adaption of arbuscular mycorrhizal symbiosis to phosphorus deficiency

Arbuscular mycorrhizal (AM) symbiosis, a ubiquitous symbiotic association established between AM fungi and roots of most higher plants in terrestrial ecosystems, is essentially important for plant adaptation to various environmental stresses, especially for phosphorus (P) deficiency. Many studies uncovered the physiological mechanisms of AM plant adaptation to P deficiency, while recent studies have reached the underlying molecular mechanisms. In this mini-review we summarized the molecular mechanism of plant and mycorrhizal fungi sensing P stress, secretion of organic acids, regulation of phosphatase and hormone biosynthesis genes, and also the potential role of P transporters, transcription factors and small molecule miRNAs in regulating the response of AM symbiosis to low P stress. We specially introduced the research progresses in: 1) the key roles of environmental P concentration as nutritional signal initiating the establishment of AM symbiotic system; 2) regulation of phytohormone balance by AM fungi and subsequent influences on plant growth and development and root architecture; 3) the involvements of plant, fungi and mycorrhiza specifically induced phosphate transporter genes in P uptake and the regulating mechanisms; 4) the important roles of transcription factors in sensing P stress and regulating the expression of functional genes, and their importance in plant tolerance to P stress. These factors are functionally distinct but also interact with each other, and constitute a complex regulatory network for plant adaptation to P stress. Future research should deep into the mechanisms of P transport at the mycorrhizal symbiotic interface, the regulation of transcription factors relevant to plant adaptation to low P stress, and the interaction of various regulatory factors. Such work would provide strong support to the development and application of mycorrhizal technology for improving plant P nutrition.