The root endophyte Piriformospora indica and the orchid mycorrhiza Sebacina vermifera (Sebacinales, Basidiomycota) are able to establish a mutualistic symbiosis with plants. Both fungi colonize the root cortex of a wide range of vascular plants, including the monocot barley (Hordeum vulgare) and the dicot Arabidopsis thaliana. Colonization by the fungi results in growth promotion and induced resistance against abiotic and biotic stresses. Fungal development in roots combines biotrophic growth in living plant cells and cell-death associated colonization of dead cortex cells. These features together with the possibility to cultivate the fungi on synthetic media reveal substantial phenotypic plasticity which is reflected in their genomic traits.
In this study, the genomes of Piriformospora indica and Sebacina vermifera were characterized. It could be shown that certain gene and functional protein domain expansions occurred in both species. These included proteins predicted to be involved in intra- and extracellular transport (Transporters), proteolysis (Peptidases), degradation of carbohydrates (Hydrolases) and non-destructive carbohydrate binding (Lectins). Additionally, a novel family of small secreted proteins was identified in P. indica which is characterized by regular distributed histidine and alanine residues and a conserved seven amino acid motif ("RSIDELD") at the C-terminus. On the other side, the number proteins involved in secondary metabolism, in particular polyketide and nonribosomal peptide synthetases, were shown to be strongly reduced in both fungi which is indicative of the non pathogenic character of P. indica and S. vermifera.
By using microarrays and RNA-sequencing, a time- and host-specific expression of genes could be shown in P. indica during colonization of barley- or Arabidopsis roots. A first comparative analyses of genes expressed in S. vermifera and P. indica during colonization of Arabidopsis suggests that defined differences exist during the colonization of this host by both analysed fungi