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Summary Fungal phytopathogens can suppress plant immune mechanisms in order to colonize living host cells. Identifying all the molecular components involved is critical for elaborating a detailed systems‐level model of plant infection probing pathogen weaknesses; yet, the hierarchy of molecular events controlling fungal responses to the plant cell is not clear.Here we show how, in the blast fungusMagnaporthe oryzae, terminating rice innate immunity requires a dynamic network of redox‐responsive E3 ubiquitin ligases targeting fungal sirtuin 2 (Sir2), an antioxidation regulator required for suppressing the host oxidative burst.Immunoblotting, immunopurification, mass spectrometry and gene functional analyses showed that Sir2 levels responded to oxidative stress via a mechanism involving ubiquitination and three antagonistic E3 ubiquitin ligases: Grr1 and Ptr1 maintained basal Sir2 levels in the absence of oxidative stress; Upl3 facilitated Sir2 accumulation in response to oxidative stress. Grr1 and Upl3 interacted directly with Sir2 in a manner that decreased and scaled with oxidative stress, respectively.DeletingUPL3depleted Sir2 during growth in rice cells, triggering host immunity and preventing infection. OverexpressingSIR2in the Δupl3mutant remediated pathogenicity. Our work reveals how redox‐responsive E3 ubiquitin ligases inM. oryzaemediate Sir2 accumulation‐dependent antioxidation to modulate plant innate immunity and host susceptibility.
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Magnaporthe oryzae nucleoside diphosphate kinase is required for metabolic homeostasis and redox‐mediated host innate immunity suppression
Abstract The fungusMagnaporthe oryzaecauses blast, the most devastating disease of cultivated rice. After penetrating the leaf cuticle,M. oryzaegrows as a biotroph in intimate contact with living rice epidermal cells before necrotic lesions develop. Biotrophic growth requires maintaining metabolic homeostasis while suppressing plant defenses, but the metabolic connections and requirements involved are largely unknown. Here, we characterized theM. oryzaenucleoside diphosphate kinase‐encoding geneNDK1and discovered it was essential for facilitating biotrophic growth by suppressing the host oxidative burst—the first line of plant defense. NDK enzymes reversibly transfer phosphate groups from tri‐ to diphosphate nucleosides. Correspondingly, intracellular nucleotide pools were perturbed inM. oryzaestrains lackingNDK1through targeted gene deletion, compared to WT. This affected metabolic homeostasis: TCA, purine and pyrimidine intermediates, and oxidized NADP+, accumulated in Δndk1. cAMP and glutathione were depleted. ROS accumulated in Δndk1hyphae. Functional appressoria developed on rice leaf sheath surfaces, but Δndk1invasive hyphal growth was restricted and redox homeostasis was perturbed, resulting in unsuppressed host oxidative bursts that triggered immunity. We conclude Ndk1 modulates intracellular nucleotide pools to maintain redox balance via metabolic homeostasis, thus quenching the host oxidative burst and suppressing rice innate immunity during biotrophy.
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- Award ID(s):
- 1758805
- PAR ID:
- 10455069
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Microbiology
- Volume:
- 114
- Issue:
- 5
- ISSN:
- 0950-382X
- Page Range / eLocation ID:
- p. 789-807
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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