Three wall-associated kinases required for rice basal immunity form protein complexes in the plasma membrane

BGPI : équipe 4International audienceReceptor-like kinases (RLKs) play key roles in disease resistance, in particular basal immunity. They recognize patterns produced by the pathogen invasion and often work as complexes in the plasma membrane. Among these RLKs, there is increasing evidence in several plant species of the key role of Wall-associated kinases (WAKs) in disease resistance. We recently showed using rice (Oryza sativa) loss-of-function mutants of three transcriptionaly co-regulated OsWAK genes that individual OsWAKs are positively required for quantitative resistance to the rice blast fungus, Magnaporthe oryzae. This finding was unexpected since WAK genes belong to large gene families where functional redundancy is expected. Here we provide evidence that this may be due to complex physical interaction between OsWAK proteins

Unravelling nutrient exchange in ectomycorrhizal symbiosis contributing to plant potassium nutrition

A major role of mutualistic interactions between plant roots and soil fungi is the improvement of plant nutrition by an equitable exchange of nutrients leading also to tolerance of environmental stress. Ectomycorrhizal symbiosis established between woody plants and soil fungi, widespread in forest ecosystems, is crucial for the plant partner to efficiently take up poorly available nutrients. Physiological studies as well as recent genome sequencing projects (Kohler et al. (2015) Nature Genet 47: 410-415) and transcriptome analyses (Doré et al. (2015) New Phytol 208: 1169-1187; Doré et al. (2017) Environ Microbiol 19:1338-1354) have allowed progress towards the identification and characterization of the symbiotic transportome (Garcia et al. (2016) Trends in Plant Science 21: 937-950). One of the major nutrients is potassium (K+ ), the most abundant cation in plant cells. We have shown improvement of potassium nutrition (Garcia et al. (2014) New Phytol 201: 951-960) under K+ shortage conditions by ectomycorrhizal symbiosis using two model species from European forests, Pinus pinaster and Hebeloma cylindrosporum. Questions are raised to identify the transport systems involved in the uptake of nutrients from the soil and in their transfer towards the plant at the symbiotic fungus-plant interface, called Hartig net. In the case of potassium (Garcia and Zimmermann (2014) Front Plant Sci 5: 337), we have identified two types of K+ transporters, Trk and HAK, as candidates to perform K+ uptake from the soil by the fungal extraradical hyphae, and two types of K+ channels, Shaker-like and TOK, that may release K+ by the hyphae of the Hartig net into the plant apoplasm. We have studied the three TOK (Two-pore Outward K+) channels identified in the genome of H. cylindrosporum, a channel family specific for fungi initially described in yeast (Ketchum et al. (1995) Nature 376: 690-695). These three TOK channels from the ectomycorrhizal fungus H. cylindrosporum belonging to two different subfamilies have been functionally characterized and localized (Carmen Guerrero-Galán et al. (2018) Env Microbiol , in press). Finally, we have analyzed whether these K+ channels might play specific roles within the fungus and within the symbiosis

Unravelling nutrient exchange in ectomycorrhizal symbiosis contributing to plant potassium nutrition

A major role of mutualistic interactions between plant roots and soil fungi is the improvement of plant nutrition by an equitable exchange of nutrients leading also to tolerance of environmental stress. Ectomycorrhizal symbiosis established between woody plants and soil fungi, widespread in forest ecosystems, is crucial for the plant partner to efficiently take up poorly available nutrients. Physiological studies as well as recent genome sequencing projects (Kohler et al. (2015) Nature Genet 47: 410-415) and transcriptome analyses (Doré et al. (2015) New Phytol 208: 1169-1187; Doré et al. (2017) Environ Microbiol 19:1338-1354) have allowed progress towards the identification and characterization of the symbiotic transportome (Garcia et al. (2016) Trends in Plant Science 21: 937-950). One of the major nutrients is potassium (K+ ), the most abundant cation in plant cells. We have shown improvement of potassium nutrition (Garcia et al. (2014) New Phytol 201: 951-960) under K+ shortage conditions by ectomycorrhizal symbiosis using two model species from European forests, Pinus pinaster and Hebeloma cylindrosporum. Questions are raised to identify the transport systems involved in the uptake of nutrients from the soil and in their transfer towards the plant at the symbiotic fungus-plant interface, called Hartig net. In the case of potassium (Garcia and Zimmermann (2014) Front Plant Sci 5: 337), we have identified two types of K+ transporters, Trk and HAK, as candidates to perform K+ uptake from the soil by the fungal extraradical hyphae, and two types of K+ channels, Shaker-like and TOK, that may release K+ by the hyphae of the Hartig net into the plant apoplasm. We have studied the three TOK (Two-pore Outward K+) channels identified in the genome of H. cylindrosporum, a channel family specific for fungi initially described in yeast (Ketchum et al. (1995) Nature 376: 690-695). These three TOK channels from the ectomycorrhizal fungus H. cylindrosporum belonging to two different subfamilies have been functionally characterized and localized (Carmen Guerrero-Galán et al. (2018) Env Microbiol , in press). Finally, we have analyzed whether these K+ channels might play specific roles within the fungus and within the symbiosis

Potassium nutrition of ectomycorrhizal Pinus pinaster: overexpression of the Hebeloma cylindrosporum HcTrk1 transporter affects the translocation of both K(+) and phosphorus in the host plant.

International audienceMycorrhizal associations are known to improve the hydro-mineral nutrition of their host plants. However, the importance of mycorrhizal symbiosis for plant potassium nutrition has so far been poorly studied. We therefore investigated the impact of the ectomycorrhizal fungus Hebeloma cylindrosporum on the potassium nutrition of Pinus pinaster and examined the involvement of the fungal potassium transporter HcTrk1. HcTrk1 transcripts and proteins were localized in ectomycorrhizas using in situ hybridization and EGFP translational fusion constructs. Importantly, an overexpression strategy was performed on a H. cylindrosporum endogenous gene in order to dissect the role of this transporter. The potassium nutrition of mycorrhizal pine plants was significantly improved under potassium-limiting conditions. Fungal strains overexpressing HcTrk1 reduced the translocation of potassium and phosphorus from the roots to the shoots of inoculated plants in mycorrhizal experiments. Furthermore, expression of HcTrk1 and the phosphate transporter HcPT1.1 were reciprocally linked to the external inorganic phosphate and potassium availability. The development of these approaches provides a deeper insight into the role of ectomycorrhizal symbiosis on host plant K(+) nutrition and in particular, the K(+) transporter HcTrk1. The work augments our knowledge of the link between potassium and phosphorus nutrition via the mycorrhizal pathway

Localization and analysis of K+ transport systems of the ectomycorrhizal model fungus Hebeloma cylindrosporum. ICOM7

Localization and analysis of K+ transport systems of the ectomycorrhizal model fungus Hebeloma cylindrosporum. ICOM7. 7th International Conference on Mycorrhiza "Mycorrhiza for All: An Under-Earth Revolution

Unravelling nutrient exchange in ectomycorrhizal symbiosis

Unravelling nutrient exchange in ectomycorrhizal symbiosis. 3rd international Molecular Mycorrhiza Meeting iMM