This study offers new perspectives on the biochemical and physiological changes that occur in wheat following a gene-for-gene interaction with the fungal pathogen Zymoseptoria tritici. The Z. tritici isolate IPO323, carries AvrStb6, while ΔAvrStb6#33, lacks AvrStb6. The wheat cultivar (cv.) Shafir, bears the corresponding resistance gene Stb6. Inoculation of cv. Shafir with these isolates results in two contrasted phenotypes, offering a unique opportunity to study the immune response caused by the recognition of AvrStb6 by Stb6. We employed a variety of methodologies to dissect the physiological and biochemical events altered in cv. Shafir, as a result of the AvrStb6-Stb6 interaction. Comparative analysis of stomatal conductance demonstrated that AvrStb6-Stb6 mediates transient stomatal closures to restrict the penetration of Zymoseptoria tritici. Tracking photosynthetic functionality through chlorophyll fluorescence imaging analysis demonstrated that AvrStb6-Stb6 retains the functionality of photosynthesis apparatus by promoting Non-Photochemical Quenching (NPQ). Furthermore, the PlantCV image analysis tool was used to compare the H2O2 accumulation and incidence of cell death (2, 4, 8, 12, 16, and 21 dpi), over Z. tritici infection. Finally, our research shows that the AvrStb6-Stb6 interaction coordinates the expression and activity of antioxidant enzymes, both enzymatic and non-enzymatic, to counteract oxidative stress. In conclusion, the Stb6-AvrStb6 interaction in the Z. tritici-wheat pathosystem triggers transient stomatal closure and maintains photosynthesis while regulating oxidative stress.

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Background Zymoseptoria tritici is the causal agent of Septoria tritici blotch, one of the most economically destructive wheat foliar diseases. Here, we investigate the physiological and molecular changes triggered in two contrastingly responding wheat cultivars upon infection by Z. tritici. To accomplish this, we combined a qPCR with a targeted quantitative HPLC technique to evaluate the expression profiles of 13 defense-related genes and to profile the polyphenolic compounds induced differentially in two applied interactions. Results Our finding indicated that five out of 13 genes were strongly up-regulated in the resistant cultivar compared with that of the susceptible one at eight days post-inoculation (dpi), corresponding to the transition phase present in the infection process of Z. tritici. Additionally, our targeted HPLC analysis demonstrated that the traced phenolic compounds were highly elevated in the susceptible cultivar infected by Z. tritici compared with that of the resistant cultivar. Finally, our quantitative histopathological study showed that H2O2 accumulated in the resistant cultivar to a higher degree compared to the susceptible one at the biotrophic and switching phase. Conclusion To sum up, we conclude that Z. tritici mediates physiological and molecular alternations upon infection of wheat plants. Furthermore, the transition phase is likely a turning point in mounting incompatibility/compatibility in Z. tritici-wheat relationship, requiring further experiments to elucidate this claim in further detail.