The Protective Fungus Inside
STRI Panama

This photomicrograph shows the stringy fungal hyphae of an endophyte growing through leaf cells.
Photo Image courtesy USDA.

The bacteria, fungi and other microorganisms living in and on human bodies — our microbiome — is getting a lot of attention as its importance to human health becomes better understood.

The same is true for plant microbiomes, especially on cultivated plants. A group of 11 researchers, five of them from STRI, recently discovered how a single fungus living inside cacao plants radically alters processes from photosynthesis to the expression of disease resistance genes.

By spraying endophyte-free cacao leaves with the dominant endophytic fungus found in healthy cacao leaves, Colletotrichum tropicale, the researchers markedly increased expression of a gene that confers disease resistance and induced changes in expression of hundreds of other genes.

“We think this usually unnoticed inhabitant of plant leaves turns on genes that protect the plant,” said Luis Mejía, first author of the paper published in Frontiers in Microbiology. “But the plant may pay a cost for this service because the fungus-inoculated plants have lower photosynthesis and altered nitrogen metabolism.”

Mejía recently finished a three-year Earl S. Tupper postdoctoral fellowship at STRI and is now employed by Panama’s government research institute INDICASAT and the University of Panama. STRI’s Allen Herre, Klaus Winter, Milton García and Sunshine Van Bael also contributed to the paper, which combines their expertise in mutualisms, plant physiology and fungal genetics.

“It’s becoming widely recognized that microbes live within the tissues of nearly all macroorganisms, from corals to insects, plants and vertebrate animals,” said Herre. “Genetic and phenotypic studies of plants are going to have to take microbial symbionts into consideration.”

Mejía L.C., Herre E.A., Sparks J.P., Winter K., García M.N., Van Bael S.A., Stitt J., Shi Z., Zhang Y., Guiltinan M.J. and Maximova S.N. 2014. Pervasive effects of a dominant foliar endophytic fungus on host genetic and phenotypic expression in a tropical tree. Front. Microbiol. 5:479. doi:10.3389/fmicb.2014.00479

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