Mutation of an Arginine Biosynthesis Gene Causes Reduced Pathogenicity in Fusarium oxysporum f. sp. melonis

Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for pathogenicity of Fusarium oxysporum f. sp. melonis. Of the 1,129 REMI transformants tested, 13 showed reduced pathogenicity on susceptible melon cultivars. One of the mutants, FMMP95–1, was an arginine auxotroph. Structural analysis of the tagged site in FMMP95-1 identified a gene, designated ARG1, which possibly encodes argininosuccinate lyase, catalyzing the last step for arginine biosynthesis. Complementation of FMMP95–1 with the ARG1 gene caused a recovery in pathogenicity, indicating that arginine auxotrophic mutation causes reduced pathogenicity in this pathogen.

Mutagenic activity of alachlor, butachlor and carbaryl to a N2-fixing cyanobacterium Nostoc muscorum

SummaryAlachlor, butachlor and carbaryl were highly toxic to the N2-fixing cyanobacterium Nostoc muscorum, when grown on solid minimal (nitrogen-free) medium. At pesticides doses allowing about 20, 50 and 60% survival of the organism, various mutations were obtained in N. muscorum, reverse mutation from het+nif– and het–nif+ auxotrophy to het+nif+ prototrophy, forward mutation for resistance to 0·37 mM L-methionine-DL-sulfoximine, and auxotrophic mutation for the achievement of carbon-auxotrophy through 5 mM methylamine-resistance. The toxic and mutagenic effects of the three pesticides were similar to those of the well known mutagen MNNG.