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The Aquaporin TcAQP1 of the Desert Truffle Terfezia claveryi Is a Membrane Pore for Water and CO₂ Transport

¹Dpto. Biología Vegetal (Botánica), Facultad de Biología, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain; ²Dpto. Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín (CSIC), Profesor Albareda, 1, Granada 18008, Spain; ³Institute of Botany, Applied Plant Science, Darmstadt University of Technology, Schnittspahnstr. 10, D-64287 Darmstadt, Germany

Terfezia claveryi is a hypogeous mycorrhizal fungus belonging to the so-called “desert truffles,” with a good record as an edible fungus and of considerable economic importance. T. claveryi improves the tolerance to water stress of the host plant Helianthemum almeriense, for which, in field conditions, symbiosis with T. claveryi is valuable for its survival. We have characterized cDNAs from T. claveryi and identified a sequence related to the aquaporin gene family. The full-length sequence was obtained by rapid amplification of cDNA ends and was named TcAQP1. This aquaporin gene encoded a functional water-channel protein, as demonstrated by heterologous expression assays in Saccharomyces cerevisiae. The mycorrhizal fungal aquaporin increased both water and CO₂ conductivity in the heterologous expression system. The expression patterns of the TcAQP1 gene in mycelium, under different water potentials, and in mycorrhizal plants are discussed. The high levels of water conductivity of TcAQP1 could be related to the adaptation of this mycorrhizal fungus to semiarid areas. The CO₂ permeability of TcAQP1 could be involved in the regulation of T. claveryi growth during presymbiotic phases, making it a good candidate to be considered a novel molecular signaling channel in mycorrhizal fungi.