Conditional promoters to investigate gene function during wheat infection by Zymoseptoria tritici

• Published in: Fungal genetics and biology 2021-01, Vol.146, p.103487-103487, Article 103487
• Main Authors: Fantozzi, Elena, Kilaru, Sreedhar, Cannon, Stuart, Schuster, Martin, Gurr, Sarah J., Steinberg, Gero
• Format: Article
• Language: English
• Subjects: Ascomycota - genetics; Ascomycota - pathogenicity; Conditional promoters; Genes, Essential - genetics; Green Fluorescent Proteins - genetics; Host-Pathogen Interactions - genetics; Plant cell wall-degrading enzymes; Plant Diseases - genetics; Plant Diseases - microbiology; Plant Leaves - genetics; Plant Leaves - microbiology; Plant-pathogen interaction; Promoter Regions, Genetic; Septoria tritici leaf blotch; Triticum - genetics; Triticum - microbiology
• ISSN: 1087-1845; 1096-0937
• DOI: 10.1016/j.fgb.2020.103487

•We analyze the activity of 5 conditional promoters in Z. tritici-infected wheat leaves.•The promoters Pnar1 and Picl1 are repressed in planta.•The promoter PlaraB is induced in hyphae during all in planta infection stages.•The promoters Pgal7 and Pex1A are not tight, but induced during late infection.•Conditional promoters respond to plant cell wall-derived sugars in the apoplast. The fungus Zymoseptoria tritici causes Septoria tritici leaf blotch, which poses a serious threat to temperate-grown wheat. Recently, we described a raft of molecular tools to study the biology of this fungus in vitro. Amongst these are 5 conditional promoters (Pnar1, Pex1A, Picl1, Pgal7, PlaraB), which allow controlled over-expression or repression of target genes in cells grown in liquid culture. However, their use in the host-pathogen interaction in planta was not tested. Here, we investigate the behaviour of these promoters by quantitative live cell imaging of green-fluorescent protein-expressing cells during 6 stages of the plant infection process. We show that Pnar1 and Picl1 are repressed in planta and demonstrate their suitability for studying essential gene expression and function in plant colonisation. The promoters Pgal7 and Pex1A are not fully-repressed in planta, but are induced during pycnidiation. This indicates the presence of inducing galactose or xylose and/or arabinose, released from the plant cell wall by the activity of fungal hydrolases. In contrast, the PlaraB promoter, which normally controls expression of an α-l-arabinofuranosidase B, is strongly induced inside the leaf. This suggests that the fungus is exposed to L-arabinose in the mesophyll apoplast. Taken together, this study establishes 2 repressible promoters (Pnar1 and Picl1) and three inducible promoters (Pgal7, Pex1A, PlaraB) for molecular studies in planta. Moreover, we provide circumstantial evidence for plant cell wall degradation during the biotrophic phase of Z. tritici infection.