Fungal Endophyte Colonization Patterns Alter Over Time in the Novel Association Between Lolium perenne and Epichloë Endophyte AR37

Abstract

Infection of the pasture grass Lolium perenne with the seed-transmitted fungal endophyte Epichloë festucae enhances its resilience to biotic and abiotic stress. Agricultural benefits of endophyte infection can be increased by generating novel symbiotic associations through inoculating L. perenne with selected Epichloë strains. Natural symbioses have coevolved over long periods. Thus, artificial symbioses will probably not have static properties, but symbionts will coadapt over time improving the fitness of the association. Here we report for the first time on temporal changes in a novel association of Epichloë strain AR37 and the L. perenne cultivar Grasslands Samson. Over nine generations, a seed maintenance program had increased the endophyte seed transmission rates to > 95% (from an initial 76%). We observed an approximately fivefold decline in endophyte biomass concentration in vegetative tissues over time (between generations 2 and 9). This indicates strong selection pressure toward reducing endophyte-related fitness costs by reducing endophyte biomass, without compromising the frequency of endophyte transmission to seed. We observed no obvious changes in tillering and only minor transcriptomic changes in infected plants over time. Functional analysis of 40 plant genes, showing continuously decreasing expression over time, suggests that adaptation of host metabolism and defense mechanisms are important for increasing the fitness of this association, and possibly fitness of such symbioses in general. Our results indicate that fitness of novel associations is likely to improve over time and that monitoring changes in novel associations can assist in identifying key features of endophyte-mediated enhancement of host fitness.

Genome Mining and Gene Expression Reveal Maytansine Biosynthetic Genes from Endophytic Communities Living inside Gymnosporia heterophylla (Eckl. and Zeyh.) Loes. and the Relationship with the Plant Biosynthetic Gene, Friedelin Synthase

“…Another recent report from Forte et al showed that a pattern of endophytes was changed over the propagation from one generation to another generation. Forte suggested that endophytes adapted to the plant’s metabolites and defense mechanisms over generation [ 40 ]. We found that the occurrence of the halogenase gene in the cloned G. heterophylla plant came from the alteration of the endophytic population, as reported by Saleh, Xiong, and Forte [ 38 , 40 ].…”

“…Forte suggested that endophytes adapted to the plant’s metabolites and defense mechanisms over generation [ 40 ]. We found that the occurrence of the halogenase gene in the cloned G. heterophylla plant came from the alteration of the endophytic population, as reported by Saleh, Xiong, and Forte [ 38 , 40 ]. Our study thus presented a new piece of evidence showing that maytansine-producible endophytes can transmit from a mother plant to a cloned plant via vegetative propagation.…”