Identification and initial characterization of effector candidate genes in the wheat fungus Zymoseptoria tritici expressed during infection

Authors: GOMEZ, SANDRA - PURDUE UNIVERSITY; MILLION, CASSIDY - U.S. DEPARTMENT OF AGRICULTURE (USDA); Helm, Matthew; JAISWAL, NAMRATA; Goodwin, Stephen - Steve

Submitted to: European Conference on Fungal Genetics Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/21/2023
Publication Date: 3/5/2023
Citation: Gomez, S.V., Million, C., Helm, M.D., Jaiswal, N., Goodwin, S.B. 2023. Identification and initial characterization of effector candidate genes in the wheat fungus Zymoseptoria tritici expressed during infection. European Conference on Fungal Genetics Proceedings. ABSTRACT.

Interpretive Summary:

Technical Abstract: Wheat is the second-most important cereal crop. It is affected by Zymoseptoria tritici, the cause of Septoria tritici blotch. This disease has an asymptomatic stage for 1–13 days, followed by a rapid transition to necrotrophy. The lifestyle of Z. tritici makes this fungal pathogen an attractive model to investigate infection phase-specific gene expression. Differential gene expression was determined in Z. tritici during a compatible interaction with the susceptible cultivar Taichung29, two incompatible interactions with the resistant cultivars Veranopolis and Israel493, and one non-host interaction with barley. Differential gene expression was calculated at 1, 3, 6, 10, 17 and 23 days after inoculation (DAI). We found 978 up-regulated genes at 1 DAI and 2,317 up-regulated genes at 3 DAI in the compatible compared to the non-host interaction, which suggests the early activation of effector genes. We found that Z. tritici activates over 1,300 genes at 10 DAI in the compatible interaction compared to the incompatible interactions which correlates with the initiation of the necrotrophic lifestyle. The enriched KEGG pathways at 1 and 3 DAI were oxidative phosphorylation, proteasome, peroxisome, glycerophospholipid metabolism and autophagy. Biosynthesis of secondary metabolites and biosynthesis of antibiotics were significantly enriched at 17 and 23 DAI. We found that Z. tritici activates 32 putative effector genes as early as 1 DAI in the compatible interaction. Many of the candidate effectors are not predicted to target specific compartments within the cell. However, ZtCE109991 and ZtCE102792 contain predicted nuclear localization signals (NLS). ZtCE3106456 contains a chloroplast transit peptide (cTP), and ZtC394290 contains a mitochondrial targeting sequence and possible cTP and NLS. Two putative effectors are Hce2 domain-containing proteins, a conserved protein family within Dothiodemycetes that induce plant necrosis. The predicted effectors are being evaluated for cell localization, immunity suppression and necrosis induction using a Nicotiana benthamiana-based heterologous expression system.