Loss of Avirulence and Reduced Pathogenicity of a Gamma-Irradiated Mutant of Fusarium oxysporum f. sp. lycopersici

Abstract

The tomato Fusarium resistance gene I-2 confers resistance to F. oxy-sporum f. sp. lycopersici race 2, which expresses the corresponding aviru-lence gene avrI-2. To elucidate the molecular basis of this gene-for-gene interaction, we initiated a search for the avrI-2 gene. Gamma irradiation mutagenesis, using (137)Cs, was performed to generate an avrI-2 mutant of F. oxysporum f. sp. lycopersici. To this end, a race 2 isolate was first transformed with a phleomycine resistance gene and a GUS marker gene in order to distinguish mutants from contaminating isolates. A total of 21,712 mutagenized colonies was tested for loss of avirulence on I-2-containing tomato seedlings. One mutant was selected that showed the expected loss of avirulence but, surprisingly, also showed reduced pathogenicity toward susceptible tomato plants. DNA analysis was subsequently used to visualize genomic changes in the mutant. Southern analysis on contour-clamped homogeneous electrophoretic field blots demonstrated a translocation of a 3.75-Mb chromosome in the mutant. Random amplified polymorphic DNA and amplified fragment length polymorphism analysis identified at least nine polymorphisms between the wild-type and mutant isolates. Most of these polymorphisms appeared as extra fragments in the mutant and contained repetitive DNA sequences.

Antimicrobial peptaibols from Trichoderma pseudokoningii induce programmed cell death in plant fungal pathogens

“…Then, we chose Fusarium oxysporum as a model system to investigate the apoptotic mechanism involved in the action of TK VI. F. oxysporum is a harmful and ubiquitous soil-borne ascomycete, and causes vascular wilt disease in more than 100 different plant species, which is difficult to control (Mes et al, 1999;Berrocal-Lobo & Molina, 2008). Our results show that TK VI induces a metacaspase-independent apoptotic PCD in parallel with the accumulation of cytoplasmic vacuoles in F. oxysporum, which reveals the antibiotic mechanism of peptaibol against plant fungal pathogens.…”

Genetic exchange of avirulence determinants and extensive karyotype rearrangements in parasexual recombinants of Fusarium oxysporum

“…Within this forma specialis several vegetative compatibility groups (VCG0030-VCG0033) have been identified (Mes 1999). Isolates within a VCG are genetically very similar, as has been shown by AFLP analysis (Mes et al 1999b), and are probably clonally related (Correll 1991;Gordon and Martyn 1997). VCG0030 contains isolates representing the three physiological races known for F. oxysporum f. sp.…”

Tomato as a model plant for plant-pathogen interactions

“…The host then mobilizes its defenses and blocks infection by the pathogen (Agrios 2005). Avirulence genomic loci and/or genes were determined in tomato pathogens such as F. fulva (Joosten & de Wit 1999), FOL (Mes et al 1999;Teunissen et al 2002;Rep et al 2004), and Pseudomonas syringae pv. tomato (Hanekamp et al 1997).…”