Endophyte-Mediated Biotic Resistance In Fine Fescues: What We Know Currently.

It is well established that the majority of plants in nature engage in a variety of symbiotic relationships with microbes. The results of such associations often can range from mutual benefits for both parties to detrimental effect on the plant host. One important interaction that has long fascinated plant breeders is the turfgrass-fungal endophyte mutualism. Agriculturally and economically significant turfgrasses such as Festuca spp. and Lolium spp. are known to harbor the Epichloë and Neotyphodium fungi in their above ground tissues. The endophyte infection is asymptomatic and typically confers benefits, notably resistance to herbivory and better drought tolerance, to its plant host. The plant in turn makes nutrients accessible to the fungal symbiont. An intriguing aspect of this mutualism is manifested in the endophyte-mediated disease resistance unique to the F. rubra (red fescue) – E. festucae interaction.

 Previous field studies have shown that the devastating dollar spot disease caused by the fungus Sclerotinia homoeocarpa is effectively hindered in endophyte-infected F. rubra and not in endophyte-free plants. Similarly, another study demonstrated that endophyte-infected F. rubra is highly toxic to chinch bugs. In order to understand the mechanisms driving these singular advantages, we generated SOLiD^TM-SAGE quantitative transcriptome libraries of clonally propagated endophyte-free and E. festucae-infected F. rubra. These samples were analyzed for differential plant gene expression. A myriad of physiological processes were found to be affected due to the presence of E. festucae with >200 differentially expressed plant transcripts. Analysis of the E. festucae data revealed that the most abundant E. festucae transcript constituted >10% of its transcriptome. Strikingly, the second most abundant endophyte transcript encodes a small secreted antifungal protein. Additional endophyte genes that may be involved in conferring biotic resistance to endophyte-infected plants were also discovered. Functional characterization of these genes is ongoing in order to gain further insight into their mechanism of action. A description of our most current findings in this area will be presented.