Abstract
In F. graminearum, the transcriptional regulator Tri6 is encoded within the trichothecene gene cluster and regulates genes involved in the biosynthesis of the secondary metabolite deoxynivalenol (DON). The Tri6 protein with its Cys2His2 zinc-finger may also conform to the class of global transcription regulators. This class of global transcriptional regulators mediate various environmental cues and generally responds to the demands of cellular metabolism. To address this issue directly, we sought to find gene targets of Tri6 in F. graminearum grown in optimal nutrient conditions. Chromatin immunoprecipitation followed by Illumina sequencing (ChIP-Seq) revealed that in addition to identifying six genes within the trichothecene gene cluster, Tri1, Tri3, Tri6, Tri7, Tri12 and Tri14, the ChIP-Seq also identified 192 additional targets potentially regulated by Tri6. Functional classification revealed that, among the annotated genes, ∼40% are associated with cellular metabolism and transport and the rest of the target genes fall into the category of signal transduction and gene expression regulation. ChIP-Seq data also revealed Tri6 has the highest affinity toward its own promoter, suggesting that this gene could be subject to self-regulation. Electro mobility shift assays (EMSA) performed on the promoter of Tri6 with purified Tri6 protein identified a minimum binding motif of GTGA repeats as a consensus sequence. Finally, expression profiling of F. graminearum grown under nitrogen-limiting conditions revealed that 49 out of 198 target genes are differentially regulated by Tri6. The identification of potential new targets together with deciphering novel binding sites for Tri6, casts new light into the role of this transcriptional regulator in the overall growth and development of F. graminearum.
Highlights
Fusarium graminearum Schwabe [telemorph Gibberella zeae (Schwein.) Petch] is the causal agent of Fusarium head blight (FHB), one of the most destructive crop diseases in temperate climes throughout the world
In F. graminearum, the transcriptional regulator Tri6 is encoded within the trichothecene gene cluster and regulates genes involved in the synthesis and transport of DON
We utilized ChIP-Seq to demonstrate that Tri6 can potentially bind to promoters and regulate genes not involved in the synthesis of DON and many of these nontrichothecene genes are involved in various aspects of cellular metabolism, including transport and energy
Summary
Fusarium graminearum Schwabe [telemorph Gibberella zeae (Schwein.) Petch] is the causal agent of Fusarium head blight (FHB), one of the most destructive crop diseases in temperate climes throughout the world. In addition to yield reduction, FHB is often associated with the accumulation of the secondary metabolite DON in grain [1]. A considerable amount of evidence gathered over many years suggested that the physiological status of the fungus and the availability of nutrients are the main contributors for secondary metabolite production [4], [5]. Other growth conditions such as pH have been shown to influence the production of secondary metabolite in numerous fungi including F. graminearum [6], [7]. Growth conditions modified by the addition of salt solutions, hydrogen peroxide, and various phytochemicals and fungicides have been shown to influence DON production [9]
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