Mechanisms of infection and response of the fungal wheat pathogenZymoseptoria triticiduring compatible, incompatible and non-host interactions

Abstract

Zymoseptoria triticiincites Septoria tritici blotch, a disease causing significant annual yield losses in wheat. To investigate infection phase-specific gene expression in the pathogen we analyzed gene expression during infection of susceptible (Taichung 29) and resistant (Veranopolis and Israel 493) wheat cultivars, plus the non-host species barley at 1, 3, 6, 10, 17 and 23 days post-inoculation (DPI). There were dramatic differences in pathogen gene expression at 10 DPI in the compatible compared to both incompatible interactions. The largest differences in pathogen gene expression occurred at 3 DPI in both compatible and incompatible interactions compared to the non-host interaction. Thirty-one putative effectors had early expression in the compatible interaction. Subsequent subcellular localization studies usingAgrobacterium-mediated transient expression inNicotiana benthamianarevealed that most candidate effectors localized to the nucleus and cytosol, and two localized to mobile cytosolic bodies, suggesting involvement in intracellular signaling or host gene regulation. Mycgr3109710, which localized to cytosolic bodies, belongs to the non-plant PR-1-like protein family implicated in virulence in other pathogens. Comparison of pathogen gene expression in resistant and susceptible hosts, in which an initial colonization is established, versus in the non-host species, allowed us to identify genes involved in establishing infection. Comparison of the compatible and incompatible interactions identified pathogen genes involved in transition from biotrophic to necrotrophic growth at 10 DPI. In addition, we contribute to the understanding of candidate effectors that are activated early during infection and might be involved in the initial plant immunity suppression.