Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis

Highlights

• We report complete mitochondrial genome sequences and corresponding mito-transcriptomes of the two related sea anemone species Anemonia viridis and Anemonia majano
• We describe structural features of group I introns in the NADH dehydrogenase 5 gene and the cytochrome oxidase I (COI) gene, the latter containing a homing endonuclease gene
• We provide support of that the intron homing endonuclease gene is expressed in a gene-fusion strategy involving exon 1 of the COI gene
• We show that the insertion-like element orfA is well expressed from sea anemone mitochondrial geneomes
• Long-term environmental stress due to low-seawater pH conditions results in up-regulation of COI and orfA gene expressions in Anemonia viridis

Abstract

The mitochondrial genomes of sea anemones are dynamic in structure. Invasion by genetic elements, such as self-catalytic group I introns or insertion-like sequences, contribute to sea anemone mitochondrial genome expansion and complexity. By using next generation sequencing we investigated the complete mtDNAs and corresponding transcriptomes of the temperate sea anemone Anemonia viridis and its closer tropical relative Anemonia majano. Two versions of fused homing endonuclease gene (HEG) organization were observed among the Actiniidae sea anemones; in-frame gene fusion and pseudo-gene fusion. We provided support for the pseudo-gene fusion organization in Anemonia species, resulting in a repressed HEG from the COI-884 group I intron. orfA, a putative protein-coding gene with insertion-like features, was present in both Anemonia species. Interestingly, orfA and COI expression were significantly up-regulated upon long-term environmental stress corresponding to low seawater pH conditions. This study provides new insights to the dynamics of sea anemone mitochondrial genome structure and function.

Chi I., Urbarova I. & Johansen S. D., in press. Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis. Gene. Article (subscription required).

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