Novel Antifungal Activity of Lolium-Associated Epichloë Endophytes

Abstract

Asexual Epichloë spp. fungal endophytes have been extensively studied for their functional secondary metabolite production. Historically, research mostly focused on understanding toxicity of endophyte-derived compounds on grazing livestock. However, endophyte-derived compounds also provide protection against invertebrate pests, disease, and other environmental stresses, which is important for ensuring yield and persistence of pastures. A preliminary screen of 30 strains using an in vitro dual culture bioassay identified 18 endophyte strains with antifungal activity. The novel strains NEA12, NEA21, and NEA23 were selected for further investigation as they are also known to produce alkaloids associated with protection against insect pests. Antifungal activity of selected endophyte strains was confirmed against three grass pathogens, Ceratobasidium sp., Dreschlera sp., and Fusarium sp., using independent isolates in an in vitro bioassay. NEA21 and NEA23 showed potent activity against Ceratobasidium sp. and NEA12 showed moderate inhibition against all three pathogens. Crude extracts from liquid cultures of NEA12 and NEA23 also inhibited growth of the phytopathogens Ceratobasidium sp. and Fusarium sp. and provided evidence that the compounds of interest are stable, constitutively expressed, and secreted. Comparative analysis of the in vitro and in planta metabolome of NEA12 and NEA23 using LCMS profile data revealed individual metabolites unique to each strain that are present in vitro and in planta. These compounds are the best candidates for the differential bioactivity observed for each strain. Novel endophyte strains show promise for endophyte-mediated control of phytopathogens impacting Lolium spp. pasture production and animal welfare.

Epichloë Fungal Endophytes—From a Biological Curiosity in Wild Grasses to an Essential Component of Resilient High Performing Ryegrass and Fescue Pastures

“…Epichloë endophytes are known to produce a large number of secondary metabolites, many in planta [ 67 , 479 ], but some at low amounts in culture [ 83 ]. Exploitation of these has not as yet been realised but may result in bioactives that have anthelmintic effects, impacts on methanogenic microbes in ruminants, and pesticidal [ 480 ] and antifungal effects [ 374 , 401 , 481 , 482 ].…”

Global Changes in Asexual Epichloë Transcriptomes during the Early Stages, from Seed to Seedling, of Symbiotum Establishment

“…Antifungal activity of SE has been observed against many pathogenic fungi and the compounds responsible for this are still unknown [ 13 ]. Hence, these genes warrant further investigation as verlamelin has a strong and broad-spectrum antifungal activity which may contribute to the bioprotection of the host.…”

“…Associations between Epichloë endophytic fungi and grasses are generally considered to be mutualistic, as both partners benefit, and the interaction occurs without inducing any pathological symptoms or injury to the host [ 8 , 9 , 10 , 11 ]. Endophyte infection can confer a variety of benefits including environmental stress tolerance (e.g., drought, cold, salt, and waterlogging), protection from both herbivory (e.g., livestock, birds, insects, nematodes), and disease through the production of bio-protective compounds [ 10 , 12 , 13 ]. Conversely, the major benefits to the endophyte include access to nutrients from the plant apoplastic space, shelter, and a mode of transmission via the seed [ 12 , 14 ].…”

“…Some aspects of grass- Epichloë interactions, such as the biosynthesis, accumulation and ecological consequences of the known secondary metabolites and enhanced stress tolerance are well characterised. However, in addition to these well-known major alkaloid classes, evidence suggests that there are other, as yet unexplored, endophytic compounds that benefit the symbiotum [ 13 , 38 ]. The involvement of yet undiscovered mechanisms such as endophyte-mediated changes in host defence chemistry, apart from the resistance provided by alkaloids has also been suggested [ 7 ].…”

Multigene Phylogeny, Diversity and Antimicrobial Potential of Endophytic Sordariomycetes From Rosa roxburghii

“…Endophytic fungi are highly diverse taxa of microorganisms that inhabit asymptomatically in healthy tissues of living plants ( Jia et al, 2016 ), and are currently not completely explored. They have increasingly received much attention due to their biological activities, such as antifungal, antibacterial, antivirus, insecticides, antioxidant, cytotoxic, alpha-glucosidase inhibitory, anti-inflammation, antidiabetic, and anticancer properties ( Deshmukh et al, 2015 ; Zhang et al, 2019 ; Fernando et al, 2020 ; Manganyi and Ateba, 2020 ; Pal et al, 2020 ; Peng et al, 2020 ; Rahaman et al, 2020 ; Agrawal et al, 2021 ). In the field of plant protection, fungal endophytes are considered as one of the most important sources of potential biocontrol agents because of antimicrobial, antivirus, insecticides, and the alleviation of abiotic stresses ( Park et al, 2017 ; Wen et al, 2019 ).…”