![]() oxysporum isolates into pathogens of their respective hosts 6, 7, 9. Horizontal transfer of the CD chromosomes from Fol4287 or Forc016 converts non-pathogenic F. The Fol isolate 4287 and the Forc isolate 016 each contain a single virulence-associated CD chromosome that is transferable to other isolates 7– 9. radicis-cucumerinum ( Forc), a cucurbit-infecting pathogen 6– 8. So far, CD chromosomes have been identified in the tomato-infecting pathogen F. oxysporum, the precise molecular mechanisms of host specificity remain unclear. Although much is known about the genetics and pathology of F. spp.) based on the susceptibility of plant species to infection. oxysporum have different host ranges and are classified into formae speciales (ff. Therefore, CD chromosomes can be crucial determinants of host specificity that are defined by phytotoxin activity or by defense against chemicals such as phytoalexins.įusarium oxysporum causes devastating diseases of more than 100 plant species, including economically important crops such as tomato, banana, and melon 5. In contrast, the CD chromosomes of Alternaria alternata and Cochliobolus carbonum harbor host-specific toxin genes 2, 4. In Fusarium solani, for example, a CD chromosome carries phytoalexin detoxifying genes 3. The functions of CD chromosomes in some plant pathogenic fungi are associated with suppression or deactivation of host-specific factors. When pathogenic fungi lack CD chromosomes, they can grow in vitro, but often exhibit attenuated or no virulence 1, 2. In plant pathogenic fungi, dispensable chromosomes that are associated with virulence are generally referred to as supernumerary, ‘B’, or conditionally dispensable (CD) chromosomes 1. ![]() Analogous to the well-characterized virulence plasmids in bacteria, the number of these dispensable chromosomes in individual isolates can vary. Pathogenic fungi often carry chromosomes that are not necessary for growth in the non-pathogenic state 1, 2. oxysporum may be determined by a pair of effector genes on a transmissible CD chromosome. This study provides insight into how host specificity of F. oxysporum isolates capable of infecting Arabidopsis, but not of other plants. The effector pair is highly conserved in F. We identified specific CD chromosomes that are required for virulence on Arabidopsis, cabbage, or both, and describe a pair of effectors encoded on one of the CD chromosomes that is required for suppression of Arabidopsis-specific phytoalexin-based immunity. Here we show that Focn has multiple CD chromosomes. conglutinans ( Focn) can infect Brassicaceae plants including Arabidopsis ( Arabidopsis thaliana) and cabbage. Among a large number of host-specific forms, F. Fusarium oxysporum causes devastating diseases of more than 100 plant species. Virulence-associated CD chromosomes carry genes encoding effectors and/or host-specific toxin biosynthesis enzymes that may contribute to determining host specificity. Many plant pathogenic fungi contain conditionally dispensable (CD) chromosomes that are associated with virulence, but not growth in vitro.
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