Within the framework of the JGI Mycorrhizal Genomics Initiative (MGI), we are sequencing a phylogenetically and ecologically diverse suite of mycorrhizal fungi (Basidiomycota and Ascomycota), which include the major clades of symbiotic species associating with trees and woody shrubs. Analyses of these genomes will provide new insights into the diversity of mechanisms for the mycorrhizal symbiosis, including ericoid-, orchidoid- and ectomycorrhizal associations. A large collaborative effort led by PI of this project, Francis Martin (INRA), aims for master publication(s) of the MGI data analysis. Researchers who wish to publish analyses using data from unpublished MGI genomes are respectfully required to contact the PI and JGI to avoid potential conflicts on data use and coordinate other publications with the MGI master paper(s).
The desert truffle
The desert truffle Terfezia boudieri Chatin (Pezizaceae) forms two types of mycorrhizal associations with its main host plant Helianthemum sessiliflorum (Cistaceae), a small perennial shrub—an ectomycorrhiza lacking a mantle and a septate endomycorrhiza. It also forms mycorrhiza with other species of this genus. The fungus is widespread throughout the Mediterranean basin, the Arabian Peninsula, Iraq, Syria, Iran and Turkey. T. boudieri produces edible fruit bodies that have served as an important food source in the arid areas of the Middle East. Indeed, descriptions of hunting for desert truffles appear on Amorite clay tablets that date back some 4,000 years.
Phylogenetic analyses of T. boudieri, using ribosomal DNA ITS sequences, revealed three cryptic species. Terfezia hyphal cells are heterokaryotic multinucleate, but a homokaryotic mycelium culture can readily be obtained by germinating spores. In a unique dual culture system, under predetermined conditions (P/auxin ratio), two different symbiotic lifestyles are formed with Cistus incanus transformed hairy roots—either septate endomycorrhiza or ectomycorrhiza. This unique system opens the way to dissect, by comparative transcriptome analyses, the mechanism controlling the transition between these two types of mycorrhiza and to identify the key genes controlling the formation of each mycorrhizal interaction. This system constitutes a reliable means for cultivating an amenable and easy-to-grow fungus, either as a free-living culture or in the two mycorrhizal lifestyles.