Isolation and characterization of a symbiosis-regulated ras from the ectomycorrhizal fungus Laccaria bicolor

Ectomycorrhizae formed by the symbiotic interaction between ectomycorrhizal fungi and plant roots play a key role in maintaining and improving the hea lth of a wide range of plants, Mycorrhizal initiation, development, and fun ctional maintenance involve morphological changes that are mediated by acti vation and suppression of several fungal and plant genes. We identified a g ene, Lbras, in the ectomycorrhizal fungus Laccaria bicolor that belongs to the ras family of genes, which has been shown in other systems to be associ ated with signaling pathways controlling cell growth and proliferation. The Lbras cDNA complemented ras2 function in Saccharomyces cerevisiae and had the ability to transform mammalian cells. Expression of Lbras, present as a single copy in the genome, was dependent upon interaction with host roots. Northern analysis showed that expression was detectable in L. bicolor 48 h after interaction as well as in the established mycorrhizal tissue. Phylog enetic analysis with other Ras proteins showed that Lbras is related most c losely to Aras of Aspergillus nidulans.