Abstract
A major cause of yield loss in wheat worldwide is the fungal pathogen Zymoseptoria tritici, a hemibiotrophic fungus which causes Septoria leaf blotch, the most destructive wheat disease in Europe. Resistance in commercial wheat varieties is poor, however, a link between reduced nitrogen availability and increased Septoria tolerance has been observed. We have shown that Septoria load is not affected by nitrogen, whilst the fungus is in its first, symptomless stage of growth. This suggests that a link between nitrogen and Septoria is only present during the necrotrophic phase of Septoria infection. Quantitative real-time PCR data demonstrated that WRKYs, a superfamily of plant-specific transcription factors, are differentially expressed in response to both reduced nitrogen and Septoria. WRKY39 was downregulated over 30-fold in response to necrotrophic stage Septoria, whilst changes in the expression of WRKY68a during the late biotrophic phase were dependent on the concentration of nitrogen under which wheat is grown. WRKY68a may therefore mediate a link between nitrogen and Septoria. The potential remains to identify key regulators in the link between nitrogen and Septoria, and as such, elucidate molecular markers for wheat breeding, or targets for molecular-based breeding approaches.
Highlights
With over 750 million tonnes produced annually, wheat is the third most produced crop globally [1]
Our results indicate that disease severity did not change when wheat was grown under reduced nitrogen conditions for 5 weeks prior to infection
This is in contrast to previous observations, where increased nitrogen was found to result in increased Septoria severity [11,13,32]
Summary
With over 750 million tonnes produced annually, wheat is the third most produced crop globally [1]. A quantitative real-time polymerase chain reaction (qPCR) was used to assess gene expression of WRKY transcription factors in wheat under different stress conditions. A two-way ANOVA shows that the interaction between nitrogen concertation and Septoria infection is significant (p = 0.010) This shows that the way in which WRKY68a expression changes in response to reduced nitrogen is dependent on whether the plant is infected with Z. tritici or not, or vice versa. This finding is perhaps more pertinently illustrated by analysing the change in gene expression in response to Septoria infection for plants grown under each nitrogen condition separately (Figure 4C). Our results indicate that disease severity did not change when wheat was grown under reduced
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