Location: Forage-animal Production ResearchTitle: Transcriptome analysis and differential expression in tall fescue harboring different endophyte strains in response to water deficit
|NAGABHYRU, PADMAJA - University Of Kentucky|
|YOUNG, CAROLYN - Noble Research Institute|
|WEST, CHARLES - Texas Tech University|
|SCHARDL, CHRISTOPHER - University Of Kentucky|
Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2019
Publication Date: 6/28/2019
Citation: Dinkins, R.D., Nagabhyru, P., Young, C., West, C., Schardl, C.L. 2019. Transcriptome analysis and differential expression in tall fescue harboring different endophyte strains in response to water deficit. The Plant Genome. 12(2):180071.
Interpretive Summary: Tall fescue is the predominant forage in the eastern US and is important in U.S. agriculture as well as a turf for yards and athletic fields. A significant factor in the exceptional fitness of tall fescue is its seed-transmissible symbiont, the fungal endophyte Epichloë coenophiala. The most common E. coenophiala strains, called common-toxic endophyte (CTE) strains, found in tall fescue in North America produce ergot alkaloids and can cause episodes of “fescue toxicosis” to grazing livestock. Development and adoption tall fescue cultivars using non-mammal-toxic endophyte (NTE) strains, is currently underway but requires additional evaluation to assess whether the endophytes will contribute to abiotic stress tolerance in these novel symbiotic combinations. To evaluate this, ARS scientists in Lexington KY, in collaboration with University of Kentucky scientists, developed tall fescue clone combinations with and without different endophyte strains. Two tall fescue clone pairs harboring the common toxic endophyte (CTE) and two clone pairs harboring novel non-toxic endophytes (NTE) strains were subjected to stress and gene expression in relation to stress was evaluated using RNA-seq next generation sequencing. The results demonstrated that the endophyte appeared to have minimal affect plant gene expression upon stress. However, a few genes were differentially regulated when comparing clones with and without the endophyte. In conclusion, the results did not support the model that the endophyte has positive effects on stress tolerance, but did suggest that presence of the endophyte may reduce expression of anti-fungal factors in the plant and may prepare the plant for stress or aid the plant during the recovery of stress. Additional studies are needed following stress treatments to determine how the presence of the endophyte might aid in the recovery from stress.
Technical Abstract: Two tall fescue (Lolium arundinaceum) plants with an Epichloë coenophiala common-toxic CTE endophyte strain, one with a non-toxic strain (NTE19), and one an Epichloë species (FaTG-4) endophyte, were evaluated together with their respective endophyte-free clones under water-withholding (stressed) conditions in the greenhouse. Based on tiller production after resumed watering, one plant showed a positive effect from the presence of the endophyte, two showed positive but non-significant trends, and one showed no significant endophyte effect. The whorls of vegetative leaf sheaths were sampled and RNA transcriptomes were analyzed by Illumina sequencing. Differentially expressed genes (DEGs) were identified as affected by genotype, water treatment (stressed or control) or endophyte (presence or absence) if they had at least 2-fold expression difference at P = 0.05. The water withholding treatment affected 38% of the plant transcripts, and these DEGs indicated the expected stress responses. Under non-stress conditions, the presence of the endophyte appeared to repress genes involved in defense response to the fungus. The DEGs affected by the presence of endophyte under stress conditions were unique to individual plant genotypes. Our results did not support the model that the endophyte has direct, positive effects on stress tolerance, but did suggest that presence of the endophyte may reduce expression of anti-fungal host factors and prime the plant genome for stress.