Search for potassium transport systems involved in arbuscular mycorrhiza-rice symbiotic interactions

International audienceArbuscular mycorrhizal fungi (AMF) develop interdependent connections with roots of about90% of plant species. These interactions increase availability as well as translocation ofnutrients (especially N and P), and thereby improve plant nutrition and growth. Moreover,resistance to a variety of stresses, among which salt stress, has been shown to be improved byAMF-plant interactions, for example in rice. Intense research to explain the molecularmechanisms of AMF-plant beneficial interactions led to the identification of phosphate andammonium transporters involved in nutrient exchanges from AMF to the plant, in several plantspecies. In spite of the importance of potassium (K+) for plant physiology, the contribution ofAMF symbiosis to plant K+ nutrition has been little documented. Over-expression of plant K+transporters has been described in Lotus japonicus and tomato in condition of AMF symbiosis.Furthermore, K+ transport systems in the AMF Rhizophagus irregularis have been identified insilico. Here, K+ nutrition in rice colonized by R. irregularis has been analyzed at molecular andphysiological levels. Surprisingly, major K+ transport systems in rice were down-regulated uponAMF interactions, suggesting strong increase in K+ availability for uptake by root cells insymbiotic conditions. Role of K+ in the relationships between rice and R. irregularis will also bediscusse

Recherche de systèmes de transport de potassium impliqués dans le transfert de K+ de la mycorhize arbusculaire au riz lors d'interactions symbiotiques

National audienceLes champignons mycorhiziens à arbuscules (CMA) développent des connexions interdépendantes avec les racines d'environ 90% des espèces végétales. Ces interactions augmentent la disponibilité ainsi que la translocation des nutriments (en particulier N et P), et améliorent ainsi la nutrition et la croissance des plantes. De plus, la résistance à une variété de stress, parmi lesquels le stress salin, s'est avérée améliorée par les interactions CMA-plante, par exemple chez le riz. Des recherches intenses pour expliquer les mécanismes moléculaires des interactions bénéfiques CMA-plante ont conduit à l'identification de transporteurs de phosphate et d'ammonium impliqués dans les échanges de nutriments du CMA vers la plante, chez plusieurs espèces végétales. Malgré l'importance du potassium (K+) pour la physiologie des plantes, la contribution de la symbiose mycorhizienne à arbuscule à la nutrition en K+ des plantes a été peu documentée. La surexpression des transporteurs de K+ végétaux a été décrite chez Lotus japonicus et la tomate en condition de symbiose mycorhizienne à arbuscule. Ici, la nutrition en K+ du riz colonisé par Rhizophagus irregulis a été analysée aux niveaux moléculaire et physiologique. Étonnamment, les principaux systèmes de transport de K+ dans le riz étaient régulés à la baisse lors des interactions AMF, suggérant une forte augmentation de la disponibilité de K+ pour l'absorption par les cellules racinaires dans des conditions symbiotiques. De plus, des systèmes de transport de K+ dans le CMA R. irregularis ont été identifiés in silico. La fonction de l’un d’entre eux a été analysée. Le rôle de K+ dans les relations entre le riz et R. irregularis sera également discuté

Arbuscular mycorrhizal fungus Rhizophagus irregularis expresses an outwardly Shaker-like channel involved in potassium nutrition of rice ( Oryza sativa L.)

Abstract Potassium (K + ) plays crucial roles in many physiological, molecular and cellular processes in plants. Direct uptake of this nutrient by root cells has been extensively investigated, however, indirect uptake of K + mediated by the interactions of the roots with fungi in the frame of a mutualistic symbiosis, also called mycorrhizal nutrient uptake pathway, is much less known. We identified an ion channel in the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis . This channel exhibits the canonical features of Shaker-like channel shared in other living kingdoms and is named RiSKC3. Transcriptionally expressed in hyphae and in arbuscules of colonized rice roots, RiSKC3 has been shown to be located in the plasma membrane. Voltage-clamp functional characterization in Xenopus oocytes revealed that RiSKC3 is endowed with outwardly-rectifying voltage-gated activity with a high selectivity for K + over sodium ions. RiSKC3 may have a role in the AM K + pathway for rice nutrition in normal and salt stress conditions. The current working model proposes that K + ions taken up by peripheral hyphae of R. irregularis are secreted towards the host root into periarbuscular space by RiSKC3. Significance Statement Mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi are beneficial for about 80% of land plants thanks to an exchange of nutrients. The AM pathway responsible for potassium (K + ) nutrition of the plant is not known. Here we uncovered a key step of this phenomenon, by functionally characterizing the first transport system in the AM fungus Rhizophagus irregularis , and we univocally demonstrated that RiSKC3 is an K + outwardly-rectifying voltage-gated Shaker-like channel