An ancient symbiotic fungal gene network revealed by comparative transcriptomics [Rirregularis_symbiotic_tissues]

Purpose: The recent publication of the fungal mutualist R. irregularis genome facilitated transcriptomic studies. We here wanted to understand the large host range of this fungus, throught its gene regulation in divergent plants Methods: mRNA from Medicago truncatula (legume), Brachypodium distachyon (grass) and Lunularia cruciata (liverwort) in association with R. irregularis were sequenced. Reads were mapped on the genome assembly with the software CLC workbench. Fungal gene expression in the different plants was compared to extra radical hyphae as a control. Results: 529, 486 and 523 R. irregularis gene were highly overexpressed (fold change >5 ; FDR <0,05 and experimental value > l10l) in M. truncatula, B. distachyon and L. cruciata, respectively. Among those genes, 262 were induced in all hosts. qPCR validation on 32 genes supported these results in an extended set of hosts (Zea mays spp parviglumis, Pisum sativum, Marchantia paleacea). Extra radical and intra radical hyphae in association with 3 phylogenetically divergent plants were produced and gene expression in the different plants were compared to gene expression in extra radical hyphae.