| Summary: | The transcription factor THCTF1 from <i>Trichoderma harzianum</i>, previously linked to the production of 6-pentyl-2<i>H</i>-pyran-2-one (6-PP) derivatives and antifungal activity against <i>Fusarium oxysporum</i>, has been related in this study to conidiation, production of an array of volatile organic compounds (VOCs) and expression of methyltransferase genes. VOCs emitted by three <i>T. harzianum</i> strains (wild type T34, transformant ΔD1-38 that is disrupted in the <i>Thctf1</i> gene encoding the transcription factor THCTF1, and ectopic integration transformant ΔJ3-16) were characterized by Proton Transfer Reaction-Quadrupole interface-Time-Of-Flight-Mass Spectrometry (PTR-Qi-TOF-MS). <i>Thctf1</i> disruption affected the production of numerous VOCs such as the antifungal volatiles 2-pentyl furan and benzaldehyde which were under-emitted, and acetoine, a plant systemic defense inductor, which was over-emitted. Biological assays show that VOCs regulated by THCTF1 are involved in the <i>T. harzianum</i> antifungal activity against <i>Botrytis cinerea</i> and in the beneficial effects leading to <i>Arabidopsis</i> plant development. The VOC blend from the disruptant ΔD1-38: (i) inhibited <i>Arabidopsis</i> seed germination for at least 26 days and (ii) when applied to <i>Arabidopsis</i> seedlings resulted in increased jasmonic acid- and salicylic acid-dependent defenses.
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