title: Phytophthora infestans effector AVR3a is essential for virulence and manipulates plant immunity by stabilizing host E3 ligase CMPG1.
abstract: Fungal and oomycete plant pathogens translocate effector proteins into host cells to establish infection. However, virulence targets and modes of action of their effectors are unknown. Effector AVR3a from potato blight pathogen Phytophthora infestans is translocated into host cells and occurs in two forms: AVR3a(KI), which is detected by potato resistance protein R3a, strongly suppresses infestin 1 (INF1)-triggered cell death (ICD), whereas AVR3a(EM), which evades recognition by R3a, weakly suppresses host ICD. Here we show that AVR3a interacts with and stabilizes host U-box E3 ligase CMPG1, which is required for ICD. In contrast, AVR3a(KI/Y147del), a mutant with a deleted C-terminal tyrosine residue that fails to suppress ICD, cannot interact with or stabilize CMPG1. CMPG1 is stabilized by the inhibitors MG132 and epoxomicin, indicating that it is degraded by the 26S proteasome. CMPG1 is degraded during ICD. However, it is stabilized by mutations in the U-box that prevent its E3 ligase activity. In stabilizing CMPG1, AVR3a thus modifies its normal activity. Remarkably, given the potential for hundreds of effector genes in the P. infestans genome, silencing Avr3a compromises P. infestans pathogenicity, suggesting that AVR3a is essential for virulence. Interestingly, Avr3a silencing can be complemented by in planta expression of Avr3a(KI) or Avr3a(EM) but not the Avr3a(KI/Y147del) mutant. Our data provide genetic evidence that AVR3a is an essential virulence factor that targets and stabilizes the plant E3 ligase CMPG1, potentially to prevent host cell death during the biotrophic phase of infection.
authors.affiliation: The Sainsbury Laboratory, John Innes Centre, Colney, Norwich NR4 7UH, UK.
authors.forename: Jorunn I B
authors.initials: JI
authors.lastname: Bos
authors.forename: Miles R
authors.initials: MR
authors.lastname: Armstrong
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Gilroy
authors.forename: Petra C
authors.initials: PC
authors.lastname: Boevink
authors.forename: Ingo
authors.initials: I
authors.lastname: Hein
authors.forename: Rosalind M
authors.initials: RM
authors.lastname: Taylor
authors.forename: Tian
authors.initials: T
authors.lastname: Zhendong
authors.forename: Stefan
authors.initials: S
authors.lastname: Engelhardt
authors.forename: Ramesh R
authors.initials: RR
authors.lastname: Vetukuri
authors.forename: Brian
authors.initials: B
authors.lastname: Harrower
authors.forename: Christina
authors.initials: C
authors.lastname: Dixelius
authors.forename: Glenn
authors.initials: G
authors.lastname: Bryan
authors.forename: Ari
authors.initials: A
authors.lastname: Sadanandom
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Whisson
authors.forename: Sophien
authors.initials: S
authors.lastname: Kamoun
authors.forename: Paul R J
authors.initials: PR
authors.lastname: Birch
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D004795:Enzyme Stability; D054884:Host-Pathogen Interactions; D008969:Molecular Sequence Data; D055750:Phytophthora infestans / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000472:pathogenicity; D011198:Solanum tuberosum / Q000201:enzymology* / Q000276:immunology* / Q000469:parasitology; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014774:Virulence
chemical_list: D020418:Algal Proteins; D044767:Ubiquitin-Protein Ligases
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