The glutathione peroxidase‐mediated reactive oxygen species resistance, fungicide sensitivity and cell wall construction in the citrus fungal pathogen Alternaria alternata

Abstract

The ability to detoxify reactive oxygen species (ROS) is critical for pathogenicity in the necrotrophic fungus Alternaria alternata. We report a glutathione peroxidase 3 (AaGPx3) involved in the complex signalling network that is essential for the detoxification of cellular stresses induced by ROS and for A. alternata pathogenesis in citrus. AaGPx3 deletion mutants displayed increased sensitivity to H2 O2 and many ROS-generating compounds. AaGPx3 is required for correct fungal development as the AaGPx3 mutant strains showed a severe reduction in conidiation. AaGPx3 mutants accumulated higher chitin content than the wild-type and were less sensitive to the cell wall-targeting compounds calcofluor white and Congo red, as well as the fungicides fludioxonil and vinclozolin, suggesting a role of the glutathione systems in fungal cell wall construction. Virulence assays revealed that AaGPx3 is required for full virulence. The expression of AaGPx3 was downregulated in fungal strains carrying defective NADPH oxidase (Nox) or the oxidative stress responsive regulators YAP1 and HOG1, all implicated in ROS resistance. These results further support the important role of ROS detoxification during A. alternata pathogenesis in citrus. Overall, our study provides genetic evidence to define the central role of AaGPx3 in the biological and pathological functions of A. alternata.

A Major Facilitator Superfamily Transporter-Mediated Resistance to Oxidative Stress and Fungicides Requires Yap1, Skn7, and MAP Kinases in the Citrus Fungal Pathogen Alternaria alternata

“…alternata was cultured from diseased leaves of Minneola tangelo and has been previously characterized [14,18]. Fungal strains defective for a Yap1 regulator (Δyap1), a Skn7 response regulator (Δskn7), a high osmolarity glycerol (Δhog1) mitogen-activated protein kinase (MAPK), a cell wall integrity MAPK (Δslt2), a Fus3 MAPK (Δfus3), and a “two component” histidine kinase (Δhsk1) were generated from the EV-MIL31 strain in previous studies [11,12,15,38,39].…”

“…A . alternata mutant strains lacking the Yap1 transcription activator, the Hog1 mitogen-activated protein (MAP) kinase, the Ssk1 regulator, the Skn7 response regulator, the NADPH oxidase (Nox), or the Gpx3 glutathione peroxidase all displayed hypersensitivity to oxidants and reduced lesion formation on citrus [11,12,14–18]. Exogenous addition of iron partially rescued H 2 O 2 sensitivity seen for Yap1 , Hog1 , Skn7 , and Nox mutants [19], indicating the important role of iron uptake in ROS resistance.…”

Gigaspora margarita with and without its endobacterium shows adaptive responses to oxidative stress

“…We can speculate that for both the lines H2O2 also acts as a signal, as it does in dried seeds (Tommasi et al 2001, El-Maarouf-Bouteau andBailly 2008) and in fungal conidia also from pathogenic fungi, where changes in the cellular oxidative status trigger germination (Breitenbach et al 2015). Since H2O2 is a strong antibacterial molecule, the question remains whether CaGg is affected by the treatment, also considering that some of the key enzymes for glutathione biosynthesis were not found in its genome (Ghignone et al, 2012 Given the relevance of AM fungi in natural and agricultural ecosystems, we propose that the data set developed for G. margarita may be a starting point for studying environmental adaptation of AM fungi to the oxidative stress that originates from the application of fungicide or herbicide (Yang et al 2016;Angelova et al 2005). 510 511 512 513 514 515 516 517 51...…”

“…On the one hand, H2O2 may act as a signal in response to injury in fungi such as Trichoderma and Rhizophagus irregularis, suggesting that fungi share a defense mechanism based on ROS-related molecules, as is common in plants and animals (Hernández-Oñate et al 2012;Fester and Hause 2005). On the other hand, environmental stimuli can lead to oxidative stress; for example, a recent study reported that the glutathione peroxidase redox system is directly involved in the resistance of Alternaria alternata to the fungicides fludioxonil and vinclozolin (Yang et al 2016). Current information on how AM fungi respond to exogenous oxidative stress is restricted to the intraradical stages of fungal development (Belmondo et al 2016;Lanfranco et al 2005), and define a scenario in which host plant-produced ROS are part of a finetuned signaling pathway necessary for fungal development.…”

Reação de híbridos de citros à inoculação com Alternaria alternata

“…A mancha marrom de alternaria (MMA) é causada pelo fungo Alternaria alternata (28,34,35); que produz uma toxina seletiva ao hospedeiro (HST), cuja suscetibilidade está restrita às tangerinas, pomelos (C. paradisi Macf), tangores (híbridos de laranja x tangerina) e alguns de seus híbridos (3,6,23,26,33,36). Os sintomas causados pela toxina caracterizam-se por lesões necrosadas em ramos, frutos, tecidos verdes imaturos ou em fase de crescimento, podendo ocorrer um desfolhamento intenso durante os períodos de maior infecção, em vista da necrose das folhas e uma redução na produção pela queda de frutos (3, 32,34,35).…”