Mala Mukherjee

Comparative genome sequence analysis underscores mycoparasitism as the ancestral life style of Trichoderma

BackgroundMycoparasitism, a lifestyle where one fungus is parasitic on another fungus, has special relevance when the prey is a plant pathogen, providing a strategy for biological control of pests for plant protection. Probably, the most studied biocontrol agents are species of the genus Hypocrea/Trichoderma.ResultsHere we report an analysis of the genome sequences of the two biocontrol species Trichoderma atroviride (teleomorph Hypocrea atroviridis) and Trichoderma virens (formerly Gliocladium virens, teleomorph Hypocrea virens), and a comparison with Trichoderma reesei (teleomorph Hypocrea jecorina). These three Trichoderma species display a remarkable conservation of gene order (78 to 96%), and a lack of active mobile elements probably due to repeat-induced point mutation. Several gene families are expanded in the two mycoparasitic species relative to T. reesei or other ascomycetes, and are overrepresented in non-syntenic genome regions. A phylogenetic analysis shows that T. reesei and T. virens are derived relative to T. atroviride. The mycoparasitism-specific genes thus arose in a common Trichoderma ancestor but were subsequently lost in T. reesei.ConclusionsThe data offer a better understanding of mycoparasitism, and thus enforce the development of improved biocontrol strains for efficient and environmentally friendly protection of plants.

A secondary metabolite biosynthesis cluster in Trichoderma virens: evidence from analysis of genes underexpressed in a mutant defective in morphogenesis and antibiotic production

A transcriptional comparison of wild type and a secondary metabolite deficient Trichoderma virens mutant resulted in the identification of six genes similar to those involved in secondary metabolism in other fungi, including four cytochrome P450 genes, one O-methyl transferase and one terpene cylase. Four of the genes (three cytochrome P450s and the cyclase) are located as a cluster. Transcript levels of three of the P450 genes, the O-methyl transferase and the terpene cyclase were measured. These genes are underexpressed in the mutant, which lacks the major secondary metabolites produced by this strain, viridin and viridiol. Expression levels of clones from the differential library with similarity to fungal trehalose synthase and a hydrophobin were also underexpressed in the mutant, while a heat shock protein hsp98 homolog was not. Based on the gene expression pattern and associated secondary metabolite profile, along with similarity to other secondary metabolism pathways in related fungi, we predict that the cluster is associated with the production of a terpene. The terpene could be viridin. This is the first report on cloning of secondary metabolism related genes from T. virens, and of their organization in a cluster, in this biocontrol fungus.

Overlapping and distinct functions of two Trichoderma virens MAP kinases in cell-wall integrity, antagonistic properties and repression of conidiation.

We have studied the functions of the Trichoderma virens TmkB, a homologue of the yeast cell-wall integrity MAP kinase Slt2, using gene knockout. The functions of TmkB were compared to those of the pathogenicity MAP kinase homologue (TmkA). Like the tmkA loss-of-function mutants, tmkB mutants exhibited reduced radial growth and constitutive conidiation in dark as well as in liquid shake cultures. The tmkB mutants, in contrast to tmkA mutants, had cell-wall integrity defects, as shown by autolysis of the mycelia and increased sensitivity to cell-wall degrading enzymes. Interestingly, the tmkB mutants were not autolytic on the synthetic Vogels minimal medium. The tmkB mutants had attenuated ability to overgrow the plant pathogen Sclerotium rolfsii, while retaining the ability to overgrow Rhizoctonia solani and Pythium spp., a phenotype also exhibited by the tmkA mutants. This first functional analysis of a cell-wall integrity MAPK in Trichoderma spp., a group of economically important fungi, shows the importance of this signaling pathway in biocontrol. Common phenotypes of the TmkA and TmkB pathways suggest that the two MAPKs may share some substrates, perhaps subunits of key transcription factors, thus dependent on two phosphorylation events for their activity.