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

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 potassium 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 StatementArbuscular mycorhizal fungus Rhizophagus irregularis expresses a Shaker-like channel, located in the plasma membrane, endowed with a strictly outwardly-rectifying voltage-gated activity with a high selectivity for potassium over sodium ions. 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 this Shaker-like channel.