Transcriptome Analysis of the Barley-Fusarium graminearumInteraction

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Abstract
Fusarium head blight (FHB) of barley (Hordeum vulgare L.) is caused by Fusarium graminearum. FHB causes yield losses and reduction in grain quality primarily due to the accumulation of trichothecene mycotoxins such as deoxynivalenol (DON). To develop an understanding of the barley-F. graminearum interaction, we examined the relationship among the infection process, DON concentration, and host transcript accumulation for 22,439 genes in spikes from the susceptible cv. Morex from 0 to 144 h after F. graminearum and water control inoculation. We detected 467 differentially accumulating barley gene transcripts in the F. graminearum-treated plants compared with the water control-treated plants. Functional annotation of the transcripts revealed a variety of infection-induced host genes encoding defense response proteins, oxidative burst-associated enzymes, and phenylpropanoid pathway enzymes. Of particular interest was the induction of transcripts encoding potential trichothecene catabolic enzymes and transporters, and the induction of the tryptophan biosynthetic and catabolic pathway enzymes. Our results define three stages of F. graminearum infection. An early stage, between 0 and 48 h after inoculation (hai), exhibited limited fungal development, low DON accumulation, and little change in the transcript accumulation status. An intermediate stage, between 48 and 96 hai, showed increased fungal development and active infection, higher DON accumulation, and increased transcript accumulation. A majority of the host gene transcripts were detected by 72 hai, suggesting that this is an important timepoint for the barley-F. graminearum interaction. A late stage also identified between 96 and 144 hai, exhibiting development of hyphal mats, high DON accumulation, and a reduction in the number of transcripts observed. Our study provides a baseline and hypothesis-generating dataset in barley during F. graminearum infection and in other grasses during pathogen infection.