Evolutionarily conserved links between regulating phosphate starvation and arbuscular mycorrhizal symbiosis in plants (EvoSymPho)

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Phosphorus (P) like nitrogen (N), is a critical nutrient required for all life. It generally occurs in small quantities in the natural environment. Therefore, P is usually considered the "limiting" nutrient in aquatic and terrestrial ecosystems, meaning that the availability of this nutrient controls the growth and productivity of aquatic and terrestrial plants, including algae. In most land plants, symbiosis with mycorrhizal fungi, and nitrogen-fixing rhizobia mainly in legumes, greatly facilitates soil P and N uptake. The development of arbuscular mycorrhiza (AM) as well as other plant symbioses depends on the common symbiosis signaling pathway (CSSP) in host plants which recognizes the microbial partner and stimulates the expression of genes required for the symbiosis. Furthermore, AM and nodulation symbioses are controlled by the P and N status of the host via interlinked response pathways. Key components of the CSSP and the phosphate starvation response (PSR) pathway are conserved between algae and land plants. However, the function of algal orthologues of PSR and CSSP components is currently unknown. Recent work has shown that the AM symbiosis is modulated downstream of the CSSP by a network of receptor kinases including surface localized, transmembrane receptor-like kinases (RLKs) and receptor-like cytoplasmic kinases (RLCKs). Our project aims to elucidate the interactions between RLK/RLCK proteins and upstream and downstream regulatory steps that are important for understanding the evolution and the molecular mechanisms of RLCKs in AM symbiosis signaling in the context of the CSSP in land plants. We plan to compare the liverwort Marchantia paleacea, which forms AM symbiosis, with the evolutionarily distant aquatic and terrestrial alga Zygnema, which belongs to the extant sister group of land plants. We expect to gain significant insight into the evolution of AM symbiosis regulation and the integration of phosphate sensing and signaling. Our project will complement other proposals within MAdLand on integrating sensing of environmental cues, downstream cellular signaling and transcriptional responses underlying complex adaptive traits for life on land.