Transcriptome analysis of Epichloë strains in tall fescue in response to drought stress

ABSTRACT

Epichloë coenophiala, a systemic fungal symbiont (endophyte) of tall fescue (Lolium arundinaceum), has been documented to confer to this grass better persistence than plants lacking the endophyte, especially under stress conditions such as drought. The response, if any, of the endophyte to imposition of stress on the host plant has not been characterized previously. Therefore, we investigated effects on gene expression by E. coenophiala and a related endophyte when plant-endophyte symbiota were subjected to acute water-deficit stress. Plants harboring different endophyte strains were grown in sand in the greenhouse, then half were deprived of water for 48 h and the other half were watered controls. RNA was isolated from different plant tissues, and mRNA sequencing (RNA-seq) was conducted to identify genes that were differentially expressed comparing stress treatment with control. We compared two different plants harboring the common toxic E. coenophiala strain (CTE) and two non–ergot-alkaloid-producing Epichloë strains in tall fescue pseudostems, and in a second experiment we compared responses of E. coenophiala CTE in plant pseudostem and crown tissues. The endophytes responded to the stress with increased expression of genes involved in oxidative stress response, oxygen radical detoxification, C-compound carbohydrate metabolism, heat shock, and cellular transport pathways. The magnitude of fungal gene responses during stress varied among plant-endophyte symbiota. Responses in pseudostems and crowns involved some common pathways as well as some tissue-specific pathways. The fungal response to water-deficit stress involved gene expression changes in similar pathways that have been documented for plant stress responses, indicating that Epichloë spp. and their host plants either coordinate stress responses or separately activate similar stress response mechanisms that work together for mutual protection.

KEYWORDS:

• Drought stress
• endophyte
• Epichloë
• fungal gene expression
• grasses
• plant tissue
• RNA sequencing
• tall fescue

ACKNOWLEDGMENTS

The authors are thankful to Troy Bass for maintaining plants in the greenhouse. The authors also acknowledge the Iowa State University DNA sequencing facility for providing sequencing services.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

FUNDING

This research was supported by the United States Department of Agriculture (USDA) National Institute for Food and Agriculture (Hatch project KY012044), and the USDA Agricultural Research Service (CRIS project 5042-21000-002-00D and Special Cooperative Agreement 2018-09140939).

Supplementary information

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