Transcriptome Analysis and Differential Expression of Tall Fescue Harboring Different Endophyte Strains Response to Water Deficit.

Tall fescue (Lolium arundinaceum = Schedonorus arundinaceus = Festuca arundinacea) is one of the most abundant cultivated pasture grass in the United States possessing good stand longevity and forage quality traits.  The persistence of tall fescue has been partly attributed to the presence of its symbiotic fungal endophyte, Epichlo‘ coenophiala, especially during periods of stress.  However, toxic alkaloids produced by the fungus have significant negative effects on animal production.  New E. coenophiala strains producing alkaloids that protect against insects, but have no negative effects on animal production, have been postulated to provide the benefits of the endophyte without the negative effects.  However, it is not known if these new E. coenophiala strains will contribute to persistence of tall fescue in the field.  To evaluate the molecular interaction and contribution of different endophyte strains in stress response, two tall fescue clones harboring the common toxic (CTE) and two non-toxic endophyte (NTE) strains along with each tall fescue genotype lacking the endophyte were evaluated under water withholding conditions in the greenhouse.   Plants subjected to the stress and controls were harvested and RNA was isolated and transcriptome analysis was done by Illumina sequencing.  Approximate 10% and 38% of the fungal and plant genes, respectively, were differentially expressed (greater than 2-fold) due to the stress treatment.  Plant genetic pathways previously associated with stress response in other species were significantly over- and under-expressed as expected due to the water withholding treatment.   While roughly 1000 genes were differentially expressed (greater than 2-fold; P<0.01) by the presence of the endophyte in the different tall fescue/endophyte combinations under stress and control conditions, no common gene, or pathway, was found across the four tall fescue endophyte combinations that would account for the tolerance of tall fescue to stress by the presence of the endophyte.