Versatility of mycoparasitic mechanisms employed by Trichoderma guizhouense against Fusarium oxysporum and other plant pathogenic fungi
The mycoparasitic fungus Trichoderma guizhouense NJAU 4742 (Harzianum clade, Hypocreales, Ascomycota) can suppress the causative agent of banana wild disease Fusarium oxysporum f. sp. cubense 4 (Foc4, Hypocreales, Ascomycota) and kill a broad range of plant pathogens.
A neutral metalloprotease gene (encoding NMP1) is required in mycotrophic interactions with Athelia rolfsii, Alternaria alternata, Foc4 and some other fungi. However, the NMP1 activity was not the only mechanism employed by NJAU 4742 against Foc4. We have observed the bursting of H2O2 production during interactions with some fungi. It possibly implicates the involvement of diffusible oxidant generated via Fenton-like chemistry in NJAU 4742 preying Foc4. A dual RNA-Seq approach was applied for a better deciphering if the interaction between the two fungi. Consistent with an important role for Fenton chemistry in cellulose depolymerization, high transcript levels and upregulation were observed for genes involved in iron homeostasis, iron reduction, and H2O2 generation. Moreover, the genes caused cell death or putative apoptotic processes in Foc4 suggested their role on mycoparasitism. NADPH oxidase (NOX) complex is vital for cellular differentiation and signalling in fungi. Combining the morphology of ∆nox1 and overexpressing nox1 mutant, transcriptome strengthened the main pattern of Fenton chemistry attacking in NJAU 4742 preying other fungi. The mechanism of detoxification of H2O2 in NJAU 4742 were explored by transcriptome and analysed in several other Trichoderma strains.
The analysis of the transcriptomic data also revealed that several polyketide synthase (pks) genes cluster for polypeptides were induced in NJAU 4742 preying Foc4. In vitro fermentation and HPLC-MS and Nuclear Magnetic Resonance allowed us to identify harzianolide, the secondary metabolite from the group of butenolides. The ascertainment of genes cluster responsible for the synthesis of harzianolide possibly extended the application of Trichoderma sp. in agriculture as this component triggers defense mechanisms in plants.