Analysis of the Mechanisms for Soilborne Plant Disease Development using REMI-Mutants of Fusarium oxysporum

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About 20 pathogenicity mutants of Fusarium oxysporum ff. sp. conglutinans (cabbage yellows pathogen ; FOC) and lycopersici (tomato wilt pathogen ; FOL) were selected from about 2500 transformants generated by restriction enzyme-mediated integration (REMI) mutagenesis.REMI10, a pathogenicity-deficient mutant of FOC, was proved that a copy of pCNS43 was inserted into the genome. The gene disrupted by the insertion of pCSN43 was rescued and the gene seemed to encode an aspartic proteinase. We designated the gene fap1. fapl disruptants of FOC carried pathogenicity to cabbage equilibrant with FOC, showed that FAP1 is not responsible to FOC for pathogenicity. Pretreatment of cabbage root with REMI10 reduced the disease incidence of yellows caused by FOC. This suggested that REMI 10 carried biocontrol activity. Behavior of green fluorescence protein (GFP)-expressing REMI10 (EGFP-REMI10) was observed under fluorescence microscope and we could see that EGFP-REMI10 penetrate into cabbage root through cuticle slower than FOC and EGFP-REMI10 did not go through the endodermis to the xylem even 14 days after inoculation.r-120, a reduced pathogenicity mutant of FOL, was also proved that a copy of pCNS43 was inserted into the genome. The gene tagged in the mutant with pCSN43 was predicted to encode a protein of 321 amino acids and designated foir1, Homology search showed its partial similarity to a chloride conductance regulatory protein of Xenopus laevis, suggesting that FOIR1 is a transmembrane protein. Although the role of FOIR1 has never been identified, it may participate to the pathogenicity in FOL, because FOIR1 deficient mutants of FOL reproduced reduced pathogenicity on tomato.