| Summary: | <p>Abstract</p> <p>Background</p> <p>The mitochondrial genome of Metazoa is usually a compact molecule without introns. Exceptions to this rule have been reported only in corals and sea anemones (Cnidaria), in which group I introns have been discovered in the <it>cox1 </it>and <it>nad5 </it>genes. Here we show several lines of evidence demonstrating that introns can also be found in the mitochondria of sponges (Porifera).</p> <p>Results</p> <p>A 2,349 bp fragment of the mitochondrial <it>cox1 </it>gene was sequenced from the sponge <it>Tetilla </it>sp. (Spirophorida). This fragment suggests the presence of a 1143 bp intron. Similar to all the cnidarian mitochondrial introns, the putative intron has group I intron characteristics. The intron is present in the <it>cox1 </it>gene and encodes a putative homing endonuclease. In order to establish the distribution of this intron in sponges, the <it>cox1 </it>gene was sequenced from several representatives of the demosponge diversity. The intron was found only in the sponge order Spirophorida. A phylogenetic analysis of the COI protein sequence and of the intron open reading frame suggests that the intron may have been transmitted horizontally from a fungus donor.</p> <p>Conclusion</p> <p>Little is known about sponge-associated fungi, although in the last few years the latter have been frequently isolated from sponges. We suggest that the horizontal gene transfer of a mitochondrial intron was facilitated by a symbiotic relationship between fungus and sponge. Ecological relationships are known to have implications at the genomic level. Here, an ecological relationship between sponge and fungus is suggested based on the genomic analysis.</p>
|
|---|
