Despite the efforts taken, phytopathogens continue to pose a severe threat to global food security, which may further increase as climate change advances. Fungal pathogens utilize a diverse repertoire of secreted molecules, termed effectors, to aid in host colonization. To date, phytopathogen research has mainly aimed at identifying bilateral interactions of effectors involved in virulence and plant proteins that enhance resistance. However, the functions of most secreted proteins and putative effectors remain elusive. Recent reports on antimicrobial effectors in fungal phytopathogens raised attention on plant microbiome-pathogen interactions. Hence, successful host microbiome manipulation may be crucial to fungal virulence. Here, we focus on the role of microbial interactions by the wheat-infecting, hemibiotrophic pathogen Zymoseptoria tritici. Recent data show upregulation of Killer protein 4-like (KP4) and Killer protein 6-like (KP6) putative effectors during the biotrophic phase of Z. tritici infection of wheat. Protein structural predictions of these proteins indicate antimicrobial properties. Thus, we aimed to functionally assess Z. tritici KP4- and KP6-like effectors by heterologous expression in the yeast Pichia pastoris. Therefore, we performed confrontation assays using effector-expressing P. pastoris strains and Z. tritici-affected wheat apoplastic bacteria. We showed that KP4- and KP6-like putative effectors of Z. tritici inhibit certain wheat apoplastic bacteria.
Pachinger et al. (Fri,) studied this question.