Potassium nutrition of ectomycorrhizal Pinus pinaster:overexpression of the Hebeloma cylindrosporum HcTrk1transporter affects the translocation of both K+ and phosphorusin the host plant

摘要

Mycorrhizal associations are known to improve the hydro-mineral nutrition of their hostplants. However, the importance of mycorrhizal symbiosis for plant potassium nutrition has sofar been poorly studied. We therefore investigated the impact of the ectomycorrhizal fungusHebeloma cylindrosporum on the potassium nutrition of Pinus pinaster and examined theinvolvement of the fungal potassium transporter HcTrk1. HcTrk1 transcripts and proteins were localized in ectomycorrhizas using in situ hybridizationand EGFP translational fusion constructs. Importantly, an overexpression strategy was performedon 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 ofpotassium and phosphorus from the roots to the shoots of inoculated plants in mycorrhizalexperiments. Furthermore, expression of HcTrk1 and the phosphate transporter HcPT1.1were reciprocally linked to the external inorganic phosphate and potassium availability. The development of these approaches provides a deeper insight into the role of ectomycorrhizalsymbiosis on host plant K+ nutrition and in particular, the K+ transporter HcTrk1. Thework augments our knowledge of the link between potassium and phosphorus nutrition viathe mycorrhizal pathway.