Biological Control

The long-term goal of my research program is to understand the interactions of Trichoderma species with pathogenic fungi as well as plant hosts to promote crop protection. My laboratory has developed a system for determining the mechanisms of biocontrol using the ubiquitous mycoparasite T. virens. The capability of T. virens to secrete hydrolytic enzymes involved in the degradation of fungal cell walls and produce antibiotic compounds that detrimentally alter fungal membranes presents an opportunity to study single and synergistic effects of these biologically active compounds. We have isolated and characterized several genes that encode for hydrolytic enzymes (chitinases, glucanases, proteinases) and antibiotics (peptaibols). Functional analysis of these genes is being conducted by genetically constructing strains of T. virens that over-express or are incapable (gene disruption) of producting the target enzymes. These novel strains are being screened for alterations in their general life stages (growth pattern, sporulation capacity, germination of spores, antibiotic profile), their interactions with pathogenic fungi, and their ability to colonize roots of plants. Another area of interest is the induction and regulation of these genes during the mycoparasitic interaction, under various substrate conditions, and as roots are colonized. These same genes can be used to construct transgenic cotton plants (as we have done with an endochitinase) for enhanced resistance to fungal pathogens. We have projects that are determining the effects of using a combination of strains each over-expressing a single enzyme, single strains constructed to over-express gene combinations or over-expression stains combined with transgenic plants on plant protection against fungal pathogens.

As several types of peptides (peptiabols, siderophores, toxins) secreted by fungi are synthesized by enzymes instead of ribosomes, we have projects to identify and characterize the non-ribosomal peptides (NRPs) from T. virens. Clearly these peptides have the potential to affect microbe-microbe and plant-microbe interactions as they appear to function in a signaling role between organisms, may directly affect the integrity of cell membranes, and promote the acquisition of iron from the environment. We have cloned several NRPs and are in the process of determining their expression patterns, interrelationships and functional role in mycoparasitism. Many species of Trichoderma are rhizosphere competent, forming a close association with the plant host. The ability to form an intimate association (invasion of epidermal cells) with a plant suggests a mechanism of recognition and/or host response. We have isolated and purified an elicitor from T. virens that is involved in the induction of host resistance mechanisms. This research has the potential for developing novel control strategies for plant pathogens as well as unraveling the mechanisms by which these host-associated fungi can colonize plants.

Vargas, W.A., Djonovic, S., Sukno, S.A., and Kenerley, C.M. 2008. Dimerization controls the activity of fungal elicitors that trigger systemic resistance in plants. Journal of Biological Chemistry 283: 19804-19825.

Kubicek, C.P., Baker, S., Gamauf, C., Kenerley, C.M., and Druzhinina, I.S. 2008. Purifying selection and birth-and-death evolution in the class II hydrophobin gene families of the ascomycete Trichoderma/Hypocrea. BMC Evolutionary Biology 8: 4 (pages 1-16).

Djonovic, S., Vargas, W.A., Kolomiets, M.V., Horndeski, M., Wiest, A., and Kenerley, C.M. 2007. A proteinaceous elicitor Sm1 from the beneficial fungus Trichoderma virens is required for induced systemic resistance in maize. Plant Physiology 145: 875-889.

Viterbo, A., Wiest, A., Brotman, Y., Ilan, C., and Kenerley, C. 2007. The 18mer peptaibols from Trichoderma virens elicit plant defense responses. Molecular Plant Pathology 8:737-746.

Djonovic,S., Vittone, G., Mendoza-Herrera, A., and Kenerley, C. 2007. Enhanced biocontrol activity of Trichoderma virens transformants constitutively co-expressing β-1,3- and β-1,6-glucanase genes. Molecular Plant Pathology 8:469-480.