Interaction of host factors in response to yeast K2 toxin stress – attractiveness for plant protection

Killer toxin-producing yeasts are important in agriculture, as they may be used for the biological control of field and post-harvest bacterial and fungal diseases of plants. The foundation for the development and application of killer yeast as plant protection agents is understanding the mechanisms underlying killer toxin-conditioned biocontrol activity and the tolerance to toxin-driven stress. This study aimed to determine the interactions between genetic effectors of cell wall integrity (CWI) and high osmolarity glycerol (HOG) pathways under the stress conditions caused by Saccharomyces cerevisiae dsRNA-originated K2 toxin. Genetic interaction studies have used different measures of fitness including the relative growth rate and toxin susceptibility. During the research, 12 double deletion mutants were created by applying homologous recombination approach, and their growth parameters and response to toxin action were analysed. Most double gene deletion strains demonstrated insignificant (less than 30%) changes in growth rate compared to single gene mutants. Only elimination of HOG1 gene in strains Δspt3 and Δspt8 resulted in significant increase of the growth rate reaching about 0.6 h-1. K2 toxin sensitivity increased in most of the double mutants, independent of the involvement of gene products into the same or different signalling pathways thus pointing to weak interactions of gene products. HOG1 mutation alters the phenotype (from resistant to sensitive) of mutants Δrlm1, Δlrg1 and Δslm4 only and are epistatic to these CWI pathway effectors. In addition to the functional analysis, network of proteins involved in K2 toxin response was generated uncovering HOG and CWI players interconnected or acting through mediators. This study deepens insight into the K2 toxin response-modulated genetic interactions and provides data important for practical application of killer yeasts.