TRANSPOSABLE ELEMENTS IN THE FUNGAL PLANT PATHOGEN FUSARIUM-OXYSPORUM

The genome of the fungal plant pathogen Fusarium oxysporum contains at least six different families of transposable elements. Representative s of both DNA transposons and retrotransposons have been identified, e ither by cloning of dispersed repetitive sequences (Foret and palm) or by trapping in the nitrate reductase gene (Fot1, Fot2, Impala and Hop ). Fot1 and Impala elements are related to the Tc1 and mariner class o f transposons. These transposable elements can affect gene structure a nd function in several ways: inactivation of the target gene through i nsertion, diversification of the nucleotide sequence by imprecise exci sions, and probably chromosomal rearrangements as suggested by the ext ensive karyotype variation observed among field isolates. Comparisons of the distribution of these elements in Fusarium populations have imp roved our understanding of population structure and epidemiology and p rovided support for horizontal genetic transfer. Also they could be de veloped as genetic tools for tagging genes, a cloning strategy that is particularly promising in imperfect fungi.