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

Abstract

ABSTRACTZymoseptoria tritici, the causal agent of septoria tritici blotch, is one of Europe’s most damaging wheat pathogens, causing significant economic losses. Genetic resistance is a common strategy to control the disease,Stb6being a resistance gene used for over 100 years in Europe. This study investigates the molecular mechanisms underlying Stb6-mediated resistance. Utilizing confocal microscopy imaging, we identified thatZ. triticiepiphytic hyphae mainly accumulates the corresponding avirulence factor AvrStb6 in close proximity to stomata. Consequently, the progression of AvrStb6-expressing avirulent strains is hampered during penetration. The fungal growth inhibition co-occurs with a transcriptional reprogramming in wheat characterized by an induction of immune responses, genes involved in stomata regulation, and cell wall-related genes. Overall, we shed light on the gene-for-gene resistance mechanisms in the wheat -Z. triticipathosystem at the cytological and transcriptomic level, and our results highlight that stomata penetration is a critical process for pathogenicity and resistance.