The effector protein Avr2 of the xylem-colonizing fungus Fusarium oxysporum activates the tomato resistance protein I-2 intracellularly.
To promote host colonization, many plant pathogens secrete effector proteins that either suppress or counteract host defences. However, when these effectors are recognized by the host's innate immune system, they trigger resistance rather than promoting virulence. Effectors are therefore key molecules in determining disease susceptibility or resistance. We show here that Avr2, secreted by the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol), shows both activities: it is required for full virulence in a susceptible host and also triggers resistance in tomato plants carrying the resistance gene I-2. Point mutations in AVR2, causing single amino acid changes, are associated with I-2-breakingFol strains. These point mutations prevent recognition by I-2, both in tomato and when both genes are co-expressed in leaves of Nicotiana benthamiana. Fol strains carrying the Avr2 variants are equally virulent, showing that virulence and avirulence functions can be uncoupled. Although Avr2 is secreted into the xylem sap when Fol colonizes tomato, the Avr2 protein can be recognized intracellularly by I-2, implying uptake by host cells.
Houterman
Petra M
PM
Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, PO Box 94062, 1090 GB Amsterdam, The Netherlands.
Ma
Lisong
L
van Ooijen
Gerben
G
de Vroomen
Marianne J
MJ
Cornelissen
Ben J C
BJ
Takken
Frank L W
FL
Rep
Martijn
M
D000595:Amino Acid Sequence; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005670:Fusarium / Q000378:metabolism* / Q000472:pathogenicity; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D007113:Immunity, Innate; D018551:Solanum lycopersicum / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D017354:Point Mutation; D014026:Nicotiana / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D014774:Virulence
D004271:DNA, Fungal; D005656:Fungal Proteins; D010940:Plant Proteins