In a recent commentary in the New Phytologists, Harman discussed how endophytic, symbiont fungi colonize plant roots without causing disease. He focused on the Trichoderma spp., a fungus used as an effective biocontrol agents to limit the growth of other plant pathogens. After the initial penetration of plant tissue, the fungus is sequestered until chemical communication, using small fungal proteins and metabolites, enables the it to grow within plant root tissue. The chemical cross talk induces systemic effects in the plant, which alters plant gene expression in beneficial ways, resulting in greater plant growth, improved seed quality and increased nitrogen use efficiency.

What appears to underpin these effects is an increase in photosynthetic efficiency in the effected plant leaf tissue.  The fungus enhanced expression of genes encoding enzymes used in several pathways in plants that convert oxidized glutathione and ascorbate to the reduced form. These antioxidants help prevent cellular damage from active oxygen species, whose formation is accelerated under increased rates of photosynthesis.

Reference: Harman, G.E. (2011) Multifunctional fungal plant symbionts: new tools to enhance plant growth and productivity, New Phytologist 189: 647–649.

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