Abstract
The major Fusarium mycotoxin deoxynivalenol (DON) is a virulence factor in wheat and has also been shown to induce defense responses in host plant tissue. In this study, global and tracer labeling with 13C were combined to annotate the overall metabolome of wheat spikes and to evaluate the response of phenylalanine-related pathways upon treatment with DON. At anthesis, spikes of resistant and susceptible cultivars as well as two related near isogenic wheat lines (NILs) differing in the presence/absence of the major resistance QTL Fhb1 were treated with 1 mg DON or water (control), and samples were collected at 0, 12, 24, 48, and 96 h after treatment (hat). A total of 172 Phe-derived wheat constituents were detected with our untargeted approach employing 13C-labeled phenylalanine and subsequently annotated as flavonoids, lignans, coumarins, benzoic acid derivatives, hydroxycinnamic acid amides (HCAAs), as well as peptides. Ninety-six hours after the DON treatment, up to 30% of the metabolites biosynthesized from Phe showed significantly increased levels compared to the control samples. Major metabolic changes included the formation of precursors of compounds implicated in cell wall reinforcement and presumed antifungal compounds. In addition, also dipeptides, which presumably are products of proteolytic degradation of truncated proteins generated in the presence of the toxin, were significantly more abundant upon DON treatment. An in-depth comparison of the two NILs with correlation clustering of time course profiles revealed some 70 DON-responsive Phe derivatives. While several flavonoids had constitutively different abundance levels between the two NILs differing in resistance, other Phe-derived metabolites such as HCAAs and hydroxycinnamoyl quinates were affected differently in the two NILs after treatment with DON. Our results suggest a strong activation of the general phenylpropanoid pathway and that coumaroyl-CoA is mainly diverted towards HCAAs in the presence of Fhb1, whereas the metabolic route to monolignol(-conjugates), lignans, and lignin seems to be favored in the absence of the Fhb1 resistance quantitative trait loci.
Highlights
Fusarium graminearum (Fg) has been ranked among the 10 most important fungal plant pathogens (Dean et al, 2012)
we have also detected a number of unknown Phe-derived metabolites
The fungus is a causal agent of the Fusarium head blight
Summary
Fusarium graminearum (Fg) has been ranked among the 10 most important fungal plant pathogens (Dean et al, 2012). The fungus is a causal agent of the Fusarium head blight (FHB) disease of small grain cereals. It starts its spread in plants in their floral tissue and, after having established an infection in the plants, results in reduced grain quality and yield and most importantly crop contamination with mycotoxins. Among the few QTL that have been characterized in more detail, most efforts have been put on the resistance locus Fusarium head blight 1 (Fhb1) (Steiner et al, 2017; Bai et al, 2018). To the present day, none of these genes has been convincingly demonstrated to be the true causal factor of Fhb or the increased resistance against the mycotoxin DON, which can not be explained by the pore-forming protein
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