Desert truffle genomes reveal their reproductive modes and new insights into plant-fungal interaction and ectendomycorrhizal lifestyle.

Desert truffles are edible hypogeous fungi forming ectendomycorrhizal symbiosis with plants of Cistaceae family. Knowledge about the reproductive modes of these fungi and the molecular mechanisms driving the ectendomycorrhizal interaction is lacking. Genomes of the highly appreciated edible desert truffles, Terfezia claveryi Chatin and Tirmania nivea Trappe, have been sequenced and compared to other Pezizomycetes. Transcriptomes of T. claveryi x Heliantemum almeriense mycorrhiza from well-watered and drought-stressed plants, when intracellular colonizations is promoted, were investigated. We have identified the fungal genes related to sexual reproduction in desert truffles and desert truffles specific genomic and secretomic features with respect to other Pezizomycetes, such as the expansion of a large set of gene families with unknown Pfam domains and a number of species or desert truffle - specific small secreted proteins differentially regulated in symbiosis. A core set of plant genes, including carbohydrate, lipid metabolism and defence related genes, differentially expressed in mycorrhiza under both conditions was found. Our results highlight the singularities of desert truffles with respect to other mycorrhizal fungi while providing a first glimpse on plant and fungal determinants involved in ecto to endo symbiotic switch that occurs in desert truffle under dry conditions.