CONTRIBUTION OF ULTRA-SHORT INVASIVE ELEMENTS TO THE EVOLUTION OF THEMITOCHONDRIAL GENOME IN THE GENUS PODOSPORA

In the filamentous fungus Podospora anserina, senescence is associated with major rearrangements of the mitochondrial DNA. The undecamer GGC GCAAGCTC has been described as a preferential site for these recombina tion events. We show that: (i) copies of this short sequence GGCGCAAGC TC are present in unexpectedly high numbers in the mitochondrial genom e of this fungus; (ii) a short cluster of this sequence, localised in a group II intronic ORF, encodes amino acids that disrupt a protein do main that is otherwise highly conserved between various species; (iii) most of the polymorphisms observed between three related species, P.a nserina, P.curvicolla and P.comata, are associated with the presence/a bsence of this sequence; (iv) this element lies at the boundaries of m ajor rearrangements of the mitochondrial genomes; (v) at least two oth er short elements in the Podaspora mitochondrial genomes display simil ar features. We suggest that these short elements, called MUSEs (mitoc hondrial ultra-short elements), could be mobile and that they contribu te to evolution of the mitochondrial genome in the genus Podospora. A model for mobility involving a target DNA-primed reverse transcription step is discussed.