Abstract
Some filamentous fungi of the Trichoderma genus are used as biocontrol agents against airborne and soilborne phytopathogens. The proposed mechanism by which Trichoderma spp. antagonizes phytopathogens is through the release of lytic enzymes, antimicrobial compounds, mycoparasitism, and the induction of systemic disease-resistance in plants. Here we analyzed the role of TGF-1 (Trichoderma Gcn Five-1), a histone acetyltransferase of Trichoderma atroviride, in mycoparasitism and antibiosis against the phytopathogen Rhizoctonia solani. Trichostatin A (TSA), a histone deacetylase inhibitor that promotes histone acetylation, slightly affected T. atroviride and R. solani growth, but not the growth of the mycoparasite over R. solani. Application of TSA to the liquid medium induced synthesis of antimicrobial compounds. Expression analysis of the mycoparasitism-related genes ech-42 and prb-1, which encode an endochitinase and a proteinase, as well as the secondary metabolism-related genes pbs-1 and tps-1, which encode a peptaibol synthetase and a terpene synthase, respectively, showed that they were regulated by TSA. A T. atroviride strain harboring a deletion of tgf-1 gene showed slow growth, thinner and less branched hyphae than the wild-type strain, whereas its ability to coil around the R. solani hyphae was not affected. Δtgf-1 presented a diminished capacity to grow over R. solani, but the ability of its mycelium -free culture filtrates (MFCF) to inhibit the phytopathogen growth was enhanced. Intriguingly, addition of TSA to the culture medium reverted the enhanced inhibition growth of Δtgf-1 MFCF on R. solani at levels compared to the wild-type MFCF grown in medium amended with TSA. The presence of R. solani mycelium in the culture medium induced similar proteinase activity in a Δtgf-1 compared to the wild-type, whereas the chitinolytic activity was higher in a Δtgf-1 mutant in the absence of R. solani, compared to the parental strain. Expression of mycoparasitism- and secondary metabolism-related genes in Δtgf-1 was differentially regulated in the presence or absence of R. solani. These results indicate that histone acetylation may play important roles in the biocontrol mechanisms of T. atroviride.
Highlights
Nucleosome, the basic unit of chromatin, consists of ~146 base pairs of DNA wrapped around a histone octamer composed of two copies of each of the core histones H2A, H2B, H3, and H4 [1]
To elucidate the involvement of chromatin acetylation on the biocontrol capacities of T. atroviride, we first assessed the effect of the histone deacetylase (HDAC) inhibitor Trichostatin A (TSA) on the growth of T. atroviride over R. solani in dual cultures
Addition of TSA to the growing medium slightly affected the growth of T. atroviride and R. solani strains (Figs 1B and 2) compared to the control without TSA (Figs 1A and 2)
Summary
Nucleosome, the basic unit of chromatin, consists of ~146 base pairs (bp) of DNA wrapped around a histone octamer composed of two copies of each of the core histones H2A, H2B, H3, and H4 [1]. Chemical modifications of histone N-terminal tails, including phosphorylation, methylation, ADPribosylation, and acetylation, among others, strongly correlate with chromatin structure and gene regulation [3]. Acetylation of lysine residues in histone N-terminal tails is related to a relaxed chromatin leading to gene transcription, whereas deacetylation is tightly associated with heterochromatin resulting in gene repression [4]. Histone acetylation is achieved by larger multisubunit complexes that are recruited by specific gene promoters to modify local chromatin structure and, regulate transcription [8]. In Neurospora crassa, the orthologous to Gcn, NGF-1 acetylates lysine 14 of histone H3 through its association with the photoreceptor White Collar-1 for light activation of the al-3 promoter [5, 15]. In Trichoderma reesei, TrGcn regulates mycelial growth, conidiation, and cellulase gene expression [10]
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