A cross-talk between harzianolide and harzianic acid, the secondary metabolites of plant beneficial Trichoderma guizhouense NJAU 4742
Harzianolide, a secondary metabolite from a group of butenolides, is secreted by Trichoderma species (Hypocreales, Ascomycota) from the Harzianum Clade. Previous studies suggest that this compound is involved in plant growth promotion and it also triggers plant defense responses. In this research, we have used HPLC/MSMS and NMR to isolate and identify harzianolide from the cultivation broth of Trichoderma guizhouense NJAU 4742 (Harzianum Clade) grown in potato dextrose broth. We also used the RNA deep sequencing and gene deletion experiment to predict and verify the cluster of secondary metabolite producing genes that are involved in harzianolide synthesis. Interestingly, the ∆pks7 mutant of T. guizhouense NJAU 4742 lacking the gene encoding polyketide synthase orthologous to the reducing PKS7 (fumonisins) sensu Baker et al. (2012), resuscitates the biosynthesis of the two isomers of harzianic acid, another plant growth promoting metabolite of Trichoderma that also has its antifungal activity. Consequently, the mutant is able to suppress the growth of several other fungi including pathogens of plants. To investigate the synthetic pathway for harzianolide, we used Saccharomyces cerevisiae BJ5464-npgA as a host for the heterologous expression of this PKS7. Thus, the combination of metabolomics and transcriptomic data points to the possible involvement of harzianolide in the regulation of secondary metabolite production in T. guizhouense.