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United States Department of Agriculture

Agricultural Research Service

Research Project: Sustainable Forage-Based Production for the Mid-South Transition Zone

Location: Forage-Animal Production Research

Title: Elucidating differences in gene expression of Epichloe coenophiala endophytic fungus in reproductive vs. vegetative tissues of tall fescue (Lolium arundinaceum)

Authors
item Nagabhyru, P -
item Dinkins, Randy
item Schardl, C -

Submitted to: American Society of Plant Biologists
Publication Type: Abstract Only
Publication Acceptance Date: March 11, 2014
Publication Date: N/A

Technical Abstract: The tall fescue – Epichloe coenophiala symbiotic system is the most extensively studied of any grass-microbe symbiosis, mainly because of its economic importance worldwide. This is also an extraordinarily stable and mutualistic symbiosis where the endophyte colonizes both vegetative and reproductive tissues of the plant. The symbiosis is constitutive and is maintained in host plant communities by seed transmission from maternal plants to progeny without causing negative effects to the host seed development. So, to elucidate this important seed transmission process and the genes that may be involved in this hereditary symbiosis, we carried out gene expression studies using “mRNA-seq” with a next-generation sequencing system. For the study, we chose three clone pairs of tall fescue with and without symbiotic endophyte, and analyzed the differential expression of both plant and fungal genes in vegetative (pseudostem) and reproductive (ovaries) tissues. The transcriptome data obtained from HiSeq was analyzed using CLCbio Genome Workbench. Transcriptome analysis of endophyte-infected versus endophyte-free tall fescue ovaries showed that expression of plant genes was not significantly different in response to the symbiont compared to the corresponding uninfected plant clones. In contrast, endophyte gene expression was dramatically different in reproductive compared to vegetative plant tissues. We identified 226 genes that were up-regulated in pseudostem tissues compared to the ovaries, largely comprising the alkaloid genes and sugar and amino acid transporter genes. In ovaries compared to pseudostem, 47 genes were up-regulated by more than 5-fold, out of which eight of the up-regulated genes were for heat-shock proteins (7-18-fold higher), suggesting a developmental switch in symbiotic fungus that is similar to heat shock in these reproductive tissues. It was also interesting that, compared to plant mRNA reads, total fungal mRNA counts were about an order of magnitude lower in ovaries than in pseudostems. We are currently testing if this difference in number of expressed genes in these tissues correlates with plant to fungal biomass ratio by using qPCR to quantify the fungus relative to plant genomic DNA. Overall, these results suggest the possibility that tall fescue plants may capture and manipulate beneficial symbionts in their reproductive tissues by reprogramming endophyte gene expression.

Last Modified: 10/20/2014
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