The wheat pathogen Zymoseptoria tritici can sense and respond to different wavelengths of light

The ascomycete fungus Zymoseptoria tritici (synonym: Mycosphaerella graminicola) is a major pathogen of wheat that causes the economically important foliar disease Septoria tritici blotch. Despite its importance as a pathogen, nothing is known about the reaction of this fungus to light. To test for light responses, cultures of Z. tritici were grown in vitro under white, blue or red light, and their transcriptomes were compared to those obtained from control cultures grown in the dark. There were huge differences in gene expression with over 3400 genes upregulated in one or more of the light conditions compared to dark, and from 1909 to 2573 genes specifically upregulated in the dark compared to the individual light treatments. Differences between light treatments were lower, ranging from only 79 differentially expressed genes in the red versus blue comparison to 585 between white light and red. Many of the differentially expressed genes had no useful annotation. For those that did, analysis of the Gene Ontology (GO) terms showed that those related to metabolism were enriched in all three light treatments, while those related to growth and communication were more prevalent in the dark. Interestingly, genes for LysM effectors that have been shown previously to be involved in pathogenicity also were upregulated in one or more of the light treatments, suggesting a possible role of light for infection. This analysis shows that Z. tritici can sense and respond to light with a huge effect on transcript abundance.