Aberrant transposition of a Tc1-mariner element, impala, in the fungus Fusarium oxysporum.
We previously determined that the impalaD transposable element of Fusarium oxysporum was able to mobilize a non autonomous copy of impala ( niaD::imp::hph), inserted in the niaD gene encoding nitrate reductase. Generally, mobilization results in the recovery of Nia(+) revertants at low frequency. In the course of this study, we recovered a transformant that gave rise to Nia(+) revertants at a high rate. These revertants displayed atypical phenotypes and showed a niaD hybridization pattern different from that in more typical revertants. Molecular analysis of the structure of the transformant and atypical revertants indicated that (i) in the transformant, two copies of impala, one defective and one active, were inserted at the same genomic locus in a head-to-head orientation; and (ii) all the revertants analyzed presented the same chromosomal rearrangement, an inversion resulting in the replacement of the niaD promoter by a new sequence containing a cryptic promoter. We also frequently observed additional DNA rearrangements (deletion or inversion) in these revertants. The sequences at the rearrangement junctions indicated the occurrence of a transposition event that used the ITRs (Inverted Terminal Repeats) of separate transposons arranged in direct orientation. These features can be interpreted as the consequences of an aberrant transposition process. Such a process may account for the rearrangements observed in some genomic regions containing multiple transposon ends, and could serve as a mechanism for the generation of genetic diversity.
Hua-Van
A
A
Institut de Génétique et Microbiologie, Unité Mixte de Recherche C8621, Bât. 400, Centre universitaire d'Orsay, 91405 Orsay, France. ahuavan@igmors.u-psud.fr
Langin
T
T
Daboussi
M-J
MJ
D001483:Base Sequence; D007446:Chromosome Inversion; D004251:DNA Transposable Elements; D004271:DNA, Fungal; D004268:DNA-Binding Proteins / Q000235:genetics*; D005670:Fusarium / Q000235:genetics*; D005800:Genes, Fungal; D010641:Phenotype; D010957:Plasmids; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019895:Transposases
D004251:DNA Transposable Elements; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C111652:mariner transposases; D019895:Transposases