title: Phosphatidylinositol monophosphate-binding interface in the oomycete RXLR effector AVR3a is required for its stability in host cells to modulate plant immunity.
abstract: The oomycete pathogen Phytophthora infestans causes potato late blight, one of the most economically damaging plant diseases worldwide. P. infestans produces AVR3a, an essential modular virulence effector with an N-terminal RXLR domain that is required for host-cell entry. In host cells, AVR3a stabilizes and inhibits the function of the E3 ubiquitin ligase CMPG1, a key factor in host immune responses including cell death triggered by the pathogen-derived elicitor protein INF1 elicitin. To elucidate the molecular basis of AVR3a effector function, we determined the structure of Phytophthora capsici AVR3a4, a close homolog of P. infestans AVR3a. Our structural and functional analyses reveal that the effector domain of AVR3a contains a conserved, positively charged patch and that this region, rather than the RXLR domain, is required for binding to phosphatidylinositol monophosphates (PIPs) in vitro. Mutations affecting PIP binding do not abolish AVR3a recognition by the resistance protein R3a but reduce its ability to suppress INF1-triggered cell death in planta. Similarly, stabilization of CMPG1 in planta is diminished by these mutations. The steady-state levels of non-PIP-binding mutant proteins in planta are reduced greatly, although these proteins are stable in vitro. Furthermore, overexpression of a phosphatidylinositol phosphate 5-kinase results in reduction of AVR3a levels in planta. Our results suggest that the PIP-binding ability of the AVR3a effector domain is essential for its accumulation inside host cells to suppress CMPG1-dependent immunity.
authors.affiliation: Plant Science Center and Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi, Yokohama, Kanagawa, 230-0045 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yaeno
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Angela
authors.initials: A
authors.lastname: Chaparro-Garcia
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schornack
authors.forename: Seizo
authors.initials: S
authors.lastname: Koshiba
authors.forename: Satoru
authors.initials: S
authors.lastname: Watanabe
authors.forename: Takanori
authors.initials: T
authors.lastname: Kigawa
authors.forename: Sophien
authors.initials: S
authors.lastname: Kamoun
authors.forename: Ken
authors.initials: K
authors.lastname: Shirasu
mesh_terms: D020816:Amino Acid Motifs; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D055750:Phytophthora infestans / Q000472:pathogenicity*; D057865:Plant Immunity; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D044767:Ubiquitin-Protein Ligases / Q000502:physiology; D037521:Virulence Factors / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*
chemical_list: C562170:AVR3a protein, Phytophthora infestans; D018129:Phosphatidylinositol Phosphates; D037521:Virulence Factors; D044767:Ubiquitin-Protein Ligases