First expressed genes inventory of endomycorrhizal fungus Gigaspora margarita as revealed by RNA-seq trascriptome analysis

Arbuscular mycorrhizal fungi (AMF, Glomeromycota), which form an ancient and widespread mutualistic symbiosis with plants, are a crucial but still enigmatic component of the plant microbiome. Despite their importance in ecology and agriculture, AMF have been slow to reveal their secrets mainly due to their status of obligate biotrophs. In the absence of a complete genome sequence, large-scale transcriptomic data on AMF are limited to the species Glomus intraradices (Tisserant et al., 2012, New Phytol. 193:755–769). To widen our knowledge on Glomeromycota biology we explored the transcriptome of Gigaspora margarita (BEG34), an AMF phylogenetically distant from G. intraradices, that also represents a specialized niche for endosymbiotic bacteria, Ca. Glomeribacter gigasporarum (Ghignone et al., 2012, ISME J. 6:136–145). Total RNAs from four fungal life stages (quiescent spores, germinated spores treated or not with strigolactones, extraradical symbiotic mycelium) were analysed through Illumina massive parallel sequencing. More than 180 million reads were obtained which were then filtered and de novo assembled with Rnnotator (JGI), a pipeline based on Velvet software. The assemblies provided the first collection of a large number of putative transcripts for a Gigaspora: here we present the draft annotation of transcripts associated to the different life stages.