The basal transcription factor II H subunit Tfb5 is required for stress response and pathogenicity in the tangerine pathotype of Alternaria alternata

Abstract

The basal transcription factor II H (TFIIH) is a multicomponent complex. In the present study, we characterized a TFIIH subunit Tfb5 by analysing loss‐ and gain‐of‐function mutants to gain a better understanding of the molecular mechanisms underlying stress resistance and pathogenicity in the citrus fungal pathogen Alternaria alternata. Tfb5 deficiency mutants (ΔAatfb5) decreased sporulation and pigmentation, and were impaired in the maintenance of colony surface hydrophobicity and cell wall integrity. ΔAatfb5 increased sensitivity to ultraviolet light, DNA‐damaging agents, and oxidants. The expression of Aatfb5 was up‐regulated in the wild type upon infection in citrus leaves, implicating the requirement of Aatfb5 in fungal pathogenesis. Biochemical and virulence assays revealed that ΔAatfb5 was defective in toxin production and cellwall‐degrading enzymes, and failed to induce necrotic lesions on detached citrus leaves. Aatfb5 fused with green fluorescent protein (GFP) was localized in the cytoplasm and nucleus and physically interacted with another subunit, Tfb2, based on yeast two‐hybrid and co‐immunoprecipitation analyses. Transcriptome and Antibiotics & Secondary Metabolite Analysis Shell (antiSMASH) analyses revealed the positive and negative roles of Aatfb5 in the production of various secondary metabolites and in the regulation of many metabolic and biosynthetic processes in A. alternata. Aatfb5 may play a negative role in oxidative phosphorylation and a positive role in peroxisome biosynthesis. Two cutinase‐coding genes (AaCut2 and AaCut15) required for full virulence were down‐regulated in ΔAatfb5. Overall, this study expands our understanding of how A. alternata uses the basal transcription factor to deal with stress and achieve successful infection in the plant host.

Peroxisomes Implicated in the Biosynthesis of Siderophores and Biotin, Cell Wall Integrity, Autophagy, and Response to Hydrogen Peroxide in the Citrus Pathogenic Fungus Alternaria alternata

“…The abilities to produce the host-selective toxin, acquire iron, degrade host cell wall, and detoxify ROS all have profound impacts on the tangerine pathotype pathogenesis. Many antioxidants are responsible for ROS detoxification, which are regulated by the Yap1 bZip transcription regulator ( Lin et al, 2009 , 2011 ; Yang et al, 2009 ), the Skn7 response regulator ( Chen et al, 2012 ), the Hog1 mitogen-activated protein kinase (MAPK; Lin and Chung, 2010 ; Chung, 2013 ; Yu et al, 2016 ), and the Tfb5 basal transcription factor II ( Fu et al, 2020 ) in the tangerine pathotype of A. alternata . ROS detoxification is also impacted by the NADPH oxidases ( Yang and Chung, 2012 , 2013 ), the major facilitator superfamily (MFS) transporters ( Chen et al, 2017 ; Lin et al, 2018 ), and the siderophore-mediated iron uptake ( Chen et al, 2013 , 2014 ; Chung et al, 2020 ), as well as the glutaredoxin and thioredoxin systems ( Yang et al, 2016 ; Ma et al, 2018 ).…”

The Multifaceted Roles of Fungal Cutinases during Infection

“…These crucial effects of cutinases during the final stage of infection have been demonstrated using a wide range of approaches, including reducing cutinase activity using synthetic chemical inhibitors, lowering its expression by mutation or genetic manipulation, and increasing its activity using ectopic integration or overexpression. For example, the chemical inhibition or mutation of cutinases reduced infection rates and cuticle penetration capacity in species belonging to the necrotrophic fungi Venturia, Verticillium, Alternaria, and Curvularia [39,62,[66][67][68]; the hemibiotrophic Fusarium, Pyrenopeziza, Magnaporthe, and Colletotrichum [29,40,42,43,49,[69][70][71][72][73]; and the biotrophic Erysiphe and Uromyces [45,52]. Although spores from some of these mutants were able to germinate on the cuticle surface, they were unable to penetrate the cuticle and their hyphal tips were augmented and abnormal, indicating ineffective penetration attempts.…”

Sclerotinia sclerotiorum SsCut1 Modulates Virulence and Cutinase Activity

“…The plant cuticle is an important component for plant–fungi interactions, so alterations to its structure and permeability might change immunity to pathogenic fungi [ 17 , 35 ]. Most plant pathogens produce cutinase to destroy the plant cuticle to facilitate their infection [ 36 , 37 , 38 , 39 , 40 ]. Cutinase (EC 3.1.1.74) is a serine esterase belonging to the α/β hydrolase superfamily, capable of breaking down cutin polyesters.…”