Illuminating how light affects the wheat fungal pathogen Zymoseptoria tritici

Light is a critical part of the environment and can cause a drastic amount of damage in the fungal cell. Understanding how phytopathogens respond to and cope with light is important for knowing how to control the diseases they cause. Despite the importance of Zymoseptoria tritici as a fungal pathogen of wheat, little is known about the reaction of this fungus to light. To test for general light responses, cultures of Z. tritici were grown in vitro under white, blue or red light, and their transcriptomes were compared with each other and to those obtained from control cultures grown in darkness. There were major differences in gene expression between the dark compared to the individual light treatments, indicating that Z. tritici can sense and respond to light. Genes for 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. To study how Z. tritici responds to light, the light-sensing protein ZtVVD was examined and a deletion mutant was generated. ZtVVD was shown to be an important gene for infection, but dispensable for most general growth and stress responses. The genome of Z. tritici showed a wide range of pathways for repairing the damage to DNA done by UV light. A phylogenetic analysis of the proteins in the photolyase/cryptochrome class of proteins revealed the presence of three photolyase proteins and one Cry-DASH cryptochrome. A deletion mutant of one photolyase, ZtPhr1, showed no developmental disruption or changes in stress response, indicating a wide range of redundancies in UV repair pathways, and the necessity of further studies in this area.