OOS 30-7 - Phyllosphere microbiota and host plant defense

Wednesday, August 9, 2017: 3:40 PM
Portland Blrm 258, Oregon Convention Center
Keith Clay1, Wesley T. Beaulieu2, Lekeah Durden2, Daniel G. Panaccione3 and Dong Wang2, (1)Department of Biology, Indiana University, Bloomington, IN, (2)Biology, Indiana University, Bloomington, IN, (3)Plant & Soil Sciences, West Virginia University, Morgantown, WV

All plants harbor a diversity of non-pathogenic microbes in above-ground tissues that range from hereditary endosymbionts transmitted across generations through seeds to environmentally-acquired symbionts forming diverse, localized infections within a single leaf. While below-ground symbionts often provide mineral nutrients to host plants, above-ground microbiota generally do not have any nutritional role. Instead, protection of hosts from natural enemies is a more common functional role, paralleling the role of some endosymbiotic bacteria in arthropods. The mechanism of protection is frequently toxin production by the symbiont, or priming of the host’s innate defense responses, as illustrated by several published examples. Our recent research has focused on the role of endosymbiotic Periglandula fungi in host defense in the morning glory family (Convolvulaceae). Specifically, we obtained seeds from 241 species within the family and tested them for the presence and concentrations of ergot alkaloids, which are produced by Periglandula symbionts. We asked whether Periglandula symbiosis and alkaloid phenotypes were correlated with host geographic origin, life history or phylogeny. In addition, we experimentally evaluated the resistance of one species, Ipomoea tricolor, to root knot nematode colonization to determine if Periglandulasymbiosis improves resistance to plant pests.


From our survey of seeds from 241 species of Convolvulaceae, we found that 56 species contained ergot alkaloids indicative of Periglandula symbiosis. Alkaloid phenotypes (identities and concentrations of individual alkaloids) ranged widely among taxa. We found a nonsignificant trend for a higher proportion of tropical species to contain ergot alkaloids than non-tropical species, but there was no relationship between latitude and alkaloid concentration. Species with larger seeds were significantly more likely to contain ergot alkaloids and at higher concentrations than species with smaller seeds. ITS-based phylogeny of 92 species (where data were available) revealed that particular clades were more likely to be symbiotic than others, but there were also sporadic occurrences of Periglandula symbiosis in largely non-symbiotic clades. Greenhouse experiments using soils with high densities of root knot nematodes demonstrated that the rate of colonization and gall formation per gram of dry weight root biomass were significantly reduced in symbiotic I. tricolor compared to non-symbiotic plants. Our results indicate that microbial symbiosis with plants can provide novel defensive chemistry for hosts and enhanced resistance to plant pests, and thereby affect multiple trophic levels and community interactions.