Light-Dependent Production of Volatile Organic Compounds in Magnaporthe oryzae Mediates Self-Inhibition and Interspecific Antagonism

Volatile organic compounds (VOCs) are valuable compounds in diverse microbial interactions with certain biotic stimuli, yet pivotal roles of any VOCs derived by the rice blast fungus, Magnaporthe oryzae, in intra- and interspecies communications have been poorly understood. Therefore, in this study, we investigated that how certain VOCs by M. oryzae affect the fungal growth of the same species and other species. Using a partitioned I-plate assays, the result showed that pre-inoculated fungal colony (sender) significantly suppressed the late arriving colony (receiver) in a time- and mediadependent manner, suggesting that VOCs may function as self-inhibition agents in regulation of fungal growth. A total of eleven compounds were identified by the gas chromatography-mass spectrometry, among which four VOCs (1-hexanol, 2-ethylhexanoyl chloride, 1-octen- 3-ol, and 3-octanol) exhibited strong self-inhibition effects. Further analysis revealed that the self-inhibition mediated by M. oryzae VOCs was enhanced under light conditions compared with darkness. Genetic approaches revealed that deletion of the MoCPKA and MoPMK1 genes reduced the self-inhibitory effects, suggesting that both genes are required for growth inhibition and that VOCs play a pivotal role in regulating turgor pressure generation and appressorium formation. In addition to self-inhibition effects, M. oryzae-mediated VOCs contributed to the interspecific antagonistic interactions with other fungal species (Aspergillus nidulans, Fusarium oxysporum f.sp. conglutinans, and Sclerotinia sclerotioum). Our data clearly demonstrated that VOCs produced by the M. oryzae under light conditions are the key factors in enhancing growth inhibition both within a species (intraspecific) and among different species (interspecific).