Abstract
The endophytic fungus Epichloë festucae is known to produce bioactive metabolites, which consequently protect the host plants from biotic and abiotic stresses. We previously found that the overexpression of vibA (a gene for transcription factor) in E. festucae strain E437 resulted in the secretion of an unknown fungicide. In the present study, the active substance was purified and chemically identified as ε-poly-L-lysine (ε-PL), which consisted of 28–34 lysine units. The productivity was 3.7-fold compared with that of the wild type strain E437. The isolated ε-PL showed inhibitory activity against the spore germination of the plant pathogens Drechslera erythrospila, Botrytis cinerea, and Phytophthora infestans at 1–10 μg/mL. We also isolated the fungal gene “epls” encoding ε-PL synthetase Epls. Overexpression of epls in the wild type strain E437 resulted in the enhanced production of ε-PL by 6.7-fold. Interestingly, overexpression of epls in the different strain E. festucae Fl1 resulted in the production of shorter ε-PL with 8–20 lysine, which exhibited a comparable antifungal activity to the longer one. The results demonstrate the first example of ε-PL synthetase gene from the eukaryotic genomes and suggest the potential of enhanced expression of vibA or/and epls genes in the Epichloë endophyte for constructing pest-tolerant plants.
Highlights
Endophytes are a heterotrophic group of microorganisms including bacteria, actinomycetes and fungi that colonize in plant tissues
Infection of the fungal endophyte E. festucae E437 to perennial ryegrass enhanced disease resistance of the host plant to the grass pathogen D. erythrospila [13], suggesting that this endophyte produces unknown bioactive metabolite(s), which is effective to suppress the infection of fungal pathogens
By culturing the transformant followed by chromatographic purification and spectroscopic analysis, the antifungal principle was identified as ε-poly-L-lysine (ε-PL) consisting of 24–35 lysine units for the first time
Summary
Endophytes are a heterotrophic group of microorganisms including bacteria, actinomycetes and fungi that colonize in plant tissues. The genus Epichloë belongs to the fourth dominant class Sordariomycetes in Ascomycete endophytic fungi [2]. Their mutual interaction benefits the host plants by protecting them from insects [3,4] and diseases [5,6] and by increasing their tolerance against environmental stresses such as drought [7]. A variety of bioactive secondary metabolites have been isolated and characterized from the Epichloë endophytes. They have been known as abundant sources of insecticide alkaloids such as loline and peramine [9]. The present study highlights the purification, chemical characterization, and biosynthesis of the unknown antifungal substance produced by the Epichloë endophyte
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