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. Representatives of both DNA transposons and retrotransposons have been identified, either 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 of transposons. These transposable elements can affect gene structure and function in several ways: inactivation of the target gene through insertion, diversification of the nucleotide sequence by imprecise excisions, and probably chromosomal rearrangements as suggested by the extensive karyotype variation observed among field isolates. Comparisons of the distribution of these elements in Fusarium populations have improved our understanding of population structure and epidemiology and provided support for horizontal genetic transfer. Also they could be developed as genetic tools for tagging genes, a cloning strategy that is particularly promising in imperfect fungi.