Mapping genomic regions associated with temperature stress in the wheat pathogen <i>Zymoseptoria tritici</i>

Climate change can alter interactions between plants and their pathogens, which could adversely affect crop production. To better understand the molecular mechanisms underlying the responses of pathogenic fungi to temperature stress, we conducted a quantitative trait loci (QTL) mapping study in the wheat pathogen Zymoseptoria tritici to identify genomic regions associated with colony growth and melanization at 3 temperatures (10, 18, and 27°C). We then identified likely candidate genes for thermal adaptation within these intervals by combining information regarding gene function, gene ontology (GO) annotation enrichment, transcriptional profile, and results from previous genome-wide association studies investigating responses to climate, temperature, and thermal adaptation. The QTL mapping, conducted for 2 separate crosses involving 4 Swiss parents, found significant QTL uniquely associated with traits measured in high and low temperatures. These intervals contained many genes known to regulate responses to temperature stress, including heat-shock proteins and proteins involved in the mitogen-activated protein kinase (MAPK) pathways, and were enriched for genes with a zinc ion binding GO annotation. We highlight the most promising candidate genes for thermal adaptation, including an ammonium transporter gene, a stress response factor (Whi1) and 2 MAPK pathway genes-SSk2 and Opy2. Future validation work on these candidate genes could provide novel insight into the molecular mechanisms underlying temperature adaptation in this important wheat pathogen.