Exploitation of the antagonistic microbes for identifying novel antifungal genes and plant disease management

Abstract

Microbes can provide useful genes that are either absent in plants or more potent in biological activity than their plant equivalent. Although studies based on mutants and targeted gene disruption have been carried out by different groups, the redundancy in the Trichoderma genome of CWDE-encoding genes has made it difficult to identify enzymes required for biocontrol independently of the strain and system used. The progress made in this area of work clearly suggest that these fungi have a variety of molecular weapon that can be used in different combinations depending on the microbe they are confronting or the plant they are colonizing. Trichoderma expressed sequence tag (EST) libraries made under a large variety of inducing conditions are being processed, and entire genome sequencing initiatives have been launched both in United States and Europe. The studies performed on the proteome of Trichoderma spp. interacting with pathogens and plants have already provided many novel data that improve our understanding on how these fungi search for pathogen, talk to the plant, and protect themselves from toxicants. Understanding the mechanism of interaction between Trichoderma spp. and the plant has provided for the first time that the opportunity to genetically increase the ability of a T. atroviride strain to induce systemic resistance. Further studies are necessary for proteins whose quantitative profile changes, e.g. by generating knockout strains for phenotypic analysis. Despite some inherent limitations, proteomics is a useful method, and an important complement to other approaches for studies of microbial interactions and identifying novel antifungal genes. The work performed so far with microbial genes indicates that a significant improvement of plant resistance may be obtained in a variety of ways, but attained mainly by producing enzymes that degrade pathogen structures, enzymes that synthesize antimicrobial compounds or selective toxins. However each approach needs a tailor made strategy to minimize any detrimental effects on the acceptor plant and the expression system. A responsible use of fungal and bacterial genes for genetic improvement should produce a minimal effect on the ecosystem and contribute safely to more productive and less chemically dependent agriculture. Work in the country on cloning and identifying new antifungal genes from microbes is scanty and more studies are required by different groups to cater to our need.