Fungal transcriptomics of symbiotic incompatibility of the endophyte Epichloë bromicola with wheat : a thesis presented in partial fulfilment of the requirements for the degree Master of Philosophy, Massey University, New Zealand
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Date
2019
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Massey University
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Abstract
The fungal endophyte Epichloë bromicola forms mutualistic symbioses with grasses of the Elymus dahuricus complex. Artificial inoculation studies have shown that E. bromicola strains AR3060 and AR3018 are also able to colonise the wheat cultivar “Monad” (Triticum aestivum). Unlike the compatible and symptomless associations they form with their native hosts, colonisation of wheat by AR3060 causes host dwarfing but the endophyte is still able to undergo its life-cycle and be vertically transmitted via seed. AR3018 infection is less compatible and causes severe stunting in wheat, followed by plant death and/or the formation of endophyte-free tillers. Little is known about the molecular events associated with compatible and incompatible endophyte-host interactions.
In this study, transcriptome analysis of compatible versus incompatible interactions between AR3060 and AR3018 with their native and non-native hosts, showed that many genes predicted to encode effector-like proteins were highly up-regulated during interactions with host plants, and metal ion-binding and transmembrane transporter-related genes were significantly enriched in a gene ontology analysis. One of the most abundant transcripts in planta encodes a LysM-domain containing protein that has high identity to Cladosporium fulvum effector Ecp6 based on its secondary and tertiary structure.
Our results indicate that Epichloë endophytes may manipulate grass physiology via the production of effector proteins to produce an environment favourable for fungal infection. Through bioinformatics approaches, 27 E. bromicola candidate effectors with potential to regulate compatibility between Epichloë fungi and their
hosts have been identified. Transient expression of effectors in non-host plants, combined with targeted gene overexpression/deletion studies, are now being conducted to explore their roles in regulating defence responses and symbiotic
interactions between Epichloë and its novel wheat host.
Long term, this study aims to facilitate fully compatible interactions between E. bromicola and wheat to enable these fungi to confer biotic and abiotic stress protection to commercial wheat.
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