Identification of plant genes putatively involved in the perception of fungal ergosterol-squalene^∞

Trichoderma biocontrol strains establish a complex network of interactions with plants,in which diverse fungal molecules are involved in the recognition of these fungi as nonpathogenic organisms.These molecules act as microbial-associated molecular patterns that trigger plant responses.Previous studies have reported the im-portance of ergosterol produced by Trichoderma spp.for the ability of these fungi to induce plant growth and de-fenses.In addition,squalene,a sterol biosynthetic inter-mediate,seems to play an important role in these inter-actions.Here,we analyzed the effect of different concentrations of ergosterol and squalene on tomato(Solanum lycopersicum)growth and on the transcription level of defense-and growth-related genes.We used an RNA-seq strategy to identify several tomato genesencoding predicted pattern recognition receptor proteins or WRKY transcription factors,both of which are puta-tively involved in the perception and response to ergo-sterol and squalene.Finally,an analysis of Arabidopsis thaliana mutants lacking the genes homologous to these tomato candidates led to the identification of a WRKY40 transcription factor that negatively regulates salicylic acid-related genes and positively regulates ethylene-and jasmonate-related genes in the presence of ergosterol and squalene.