Trichoderma spp. are a rich source of secondary metabolites and volatile organic compounds (VOCs), which may induce plant defenses and modulate plant growth. In filamentous fungi, chromatin modifications regulate secondary metabolism. In this study we investigated how the absence of histone deacetylase HDA-2 in the Trichoderma atroviride strain Dhda-2 impacts its effect on a host, Arabidopsis (Arabidopsis thaliana). The production of VOCs and their impact on plant growth and development were assessed as well. The Dhda-2 strain was impaired in its ability to colonize Arabidopsis roots, thus affecting the promotion of plant growth and modulation of plant defenses against foliar pathogens Botrytis cinerea and Pseudomonas syringae, which normally result from interaction with T. atroviride. Furthermore, Dhda-2 VOCs were incapable of triggering plant defenses to counterattack foliar pathogens. The Dhda-2 overproduced the VOC 6-pentyl-2H-pyran-2-one (6-PP), which resulted in enhanced root branching and differentially regulated phytohormone-related genes. Analysis of ten VOCs (including 6-PP) revealed that three of them positively regulated plant growth, whereas six had the opposite effect. Assessment of secondary metabolites, detoxification, and communication with plant-related genes showed a dual role for HDA-2 in T. atroviride gene expression regulation during its interaction with plants. Chromatin immunoprecipitation of acetylated histone H3 on the promoters of plant-responsive genes in Dhda-2 showed, in the presence of Arabidopsis, low levels of epl-1 and abc-2 compared with that in the wild type; whereas ctf-1 presented high constitutive levels, supporting a dual role of HDA-2 in gene regulation. This work highlights the importance of HDA-2 as a global regulator in Trichoderma to modulate multiple responses in Arabidopsis. Phytohormones are small, signaling molecules, which occur at low concentrations and play pivotal roles in plants, including influencing plant growth and development. Classical phytohormones comprise auxins, abscisic acid, cytokinins, ethylene (ET), and gibberellic acid. However, brassinosteroids, jasmonates (JAs), and salicylic acid (SA) are considered phytohormones as well. These signaling molecules not only integrate, but also transmit environmental signals and modulate responses to abiotic and biotic stresses (Pieterse et al., 2009; De Bruyne et al., 2014). In their natural environments, plants interact with a plethora of microorganisms, establishing pathogenic or beneficial relationships. The plant response against these microbes lies primarily in an array of structural barriers or inducible defenses. The plant immune system has the ability to perceive nonself by recognizing pathogen-or microbe-associated molecular patterns (PAMPs or MAMPs, respectively), and translate this perception into an appropriate adaptive response (Pieterse et al., 2009). Plants have developed the ability to enhance their basal resistance after PAMPs or MAMPs are detected, by triggering the systemic acquired resistanc...

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Trichoderma spp. are filamentous fungi that colonize plant roots conferring beneficial effects to plants, either indirectly through the induction of their defense systems or directly through the suppression of phytopathogens in the rhizosphere. Transcriptomic analyses of Trichoderma spp. emerged as a powerful method for identifying the molecular events underlying the establishment of this beneficial relationship. Here, we focus on the transcriptomic response of Trichoderma virens during its interaction with Arabidopsis seedlings. The main response of T. virens to cocultivation with Arabidopsis was the repression of gene expression. The biological processes of transport and metabolism of carbohydrates were downregulated, including a set of cell wall–degrading enzymes putatively relevant for root colonization. Repression of such genes reached their basal levels at later times in the interaction, when genes belonging to the biological process of copper ion transport were induced, a necessary process providing copper as a cofactor for cell wall–degrading enzymes with the auxiliary activities class. RNA-Seq analyses showed the induction of a member of the SNF2 family of chromatin remodelers/helicase-related proteins, which was named IPA-1 (increased protection of Arabidopsis-1). Sequence analyses of IPA-1 showed its closest relatives to be members of the Rad5/Rad16 and SNF2 subfamilies; however, it grouped into a different clade. Although deletion of IPA-1 in T. virens did not affect its growth, the antibiotic activity of Δipa-1 culture filtrates against Rhizoctonia solani diminished but it remained unaltered against Botrytis cinerea. Triggering of the plant defense genes in plants treated with Δipa-1 was higher, showing enhanced resistance against Pseudomonas syringae but not against B. cinerea as compared with the wild type.

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