Stb6 mediates stomatal immunity, photosynthetic functionality, and the antioxidant system during the Zymoseptoria tritici-wheat interaction

Abstract

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.

The apoplastic space of two wheat genotypes provide highly different environment for pathogen colonization: Insights from proteome and microbiome profiling

“…1D-F and Table S5). This finding aligns with a previous study demonstrating that the interaction between AvrStb6 and Stb6 proteins in resistant wheat preserves the efficacy of the photosynthesis apparatus (24). Our findings provide novel evidence for the impact of Z. tritici on basal physiological processes, beyond defense, in the infected plant tissue during biotrophic colonization of the fungus.…”

“…Among these resistance loci the best characterized is Stb6, which confers resistance towards Z. tritici isolates by the secretion of the AvrStb6 protein (17,22,23). In resistant wheat varieties harboring Stb6, the recognition of AvrStb6 in Z. tritici isolates occurs via guard-cell located in the stomata, preventing fungal invasion and colonization (24). Hereby, recognition of Z. tritici induces a strong up-regulation of local and systemic defense responses involving the production of ROS and other defense related compounds, as well as lignin accumulation (10).…”

The Zymoseptoria tritici avirulence factor AvrStb6 accumulates in hyphae close to stomata and triggers a wheat defense response hindering fungal penetration

“…Plants regulate stomatal opening upon a pathogen attack to prevent penetration by those pathogens that use natural openings, indicating that pathogen detection through stomata is a general defensive strategy (Melotto et al 2017; Wu and Liu 2022). Noticeably, it was recently reported that AvrStb16 and Avr3D1 recognition also block avirulent isolates during wheat invasion through stomata and that wheat stomata were closed following recognition of Z. tritici strains expressing AvrStb16 or AvrStb6 (Saintenac et al 2021; Battache et al 2022; Ghiasi Noei et al 2022; Meile et al 2023). We propose that AvrStb6 recognition occurs at the stomata and that resistance proteins recognizing Avr3D1, AvrStb6 and AvrStb16 are expressed in both guard cells and subsidiary cells.…”

“…The wheat resistance gene Stb16q , encoding for a cysteine-rich protein kinase, and recognition of the avirulence factor Avr3D1 prevent Z. tritici penetration through the stomata (Saintenac et al 2021; Battache et al 2022; Meile et al 2023). In addition, it was recently demonstrated that stomatal closure is associated with Stb16q- and Stb6-mediated resistance (Battache et al 2022; Ghiasi Noei et al 2022) and that wounding partially enables infection by avirulent strains (Battache et al 2022; Bernasconi et al 2023). A better understanding of Stb6-mediated resistance mechanisms against Z. tritici invasion would provide us with novel tools to improve control methods against Z. tritici .…”

An array ofZymoseptoria triticieffectors suppress plant immune responses

“…The avirulence effector, AvrStb6 , is expressed during stomatal penetration. In wheat cultivars with AvrStb6’s corresponding resistance receptor, Stb6, infection is hindered at this early stage when the fungus grows through the stomatal opening 50,51 . A similarly timed phenotype is observed for another resistance to Z. tritici receptor, Stb16q 52 .…”