Molecular mechanisms of communication mediated by fungal volatile organic compounds

Abstract

Trichodermaspecies are soil-borne filamentous fungi widely utilized for their many plant health benefits.Trichoderma spp. establish associations with plants, nematodes and other fungi, including plant pathogens. In these interactions diverse molecules, such as microbial volatile organic compounds (mVOCs) have an important role during this inter- and intra- kingdom communication. Diverse species of Trichoderma produce different blends of mVOCs and are also differences between isolates from the same species, most likely in the capacity to respond to the environment. Here, we present the role of reactive oxygen species in T.atroviride and how mVOCs affect plant and plant pathogen interactions. By using gene deletion mutants in T. atroviride we demostrated that ?nox1, ?noxR and ?nox2 strains showed quantitative differences in the emission of several volatile organic compounds (VOCs). The effects of a blend of these volatiles on plant-growth promotion of Arabidopsis thaliana seedlings were determined in closed-chamber experiments. The increase in root and shoot biomass induced byT. atroviride VOCs was significantly lowered by ?noxR and ?nox1, but not by ?nox2. In terms of fungistatic activity at a distance, ?nox2 had a significant reduction in this trait against R. solani andS. sclerotiorum, while fungistasis was highly increased by ?noxR and ?nox1. Identification and quantification of individual VOCs in the blends emitted by the strains was performed by GC-MS, and the patterns of variation observed for individual volatiles, such as 6-Pentyl-2H-pyran-2-one (6PP-1) and (E)-6-Pent-1-enylpyran-2-one (6PP-2) were consistent with their negative effects on plant-growth promotion and positive effects on fungistasis at a distance. Nox1 and NoxR appear to have a ubiquitous regulatory role in a variety of developmental and interactive processes in T. atroviride,either as positive or negative modulators. Nox2 may also have a role in regulating production of VOCs with fungistatic activity.