Evolution of cox2 introns in angiosperm mitochondria and efficient splicing of an elongated cox2i691 intron. 2023

Alejandro A Edera, and Katharine A Howell, and Paul G Nevill, and Ian Small, and M Virginia Sanchez-Puerta
Research Institute for Signals, Systems and Computational Intelligence, sinc(i), FICH-UNL, CONICET, Ciudad Universitaria UNL, 3000 Santa Fe, Argentina. Electronic address: aedera@sinc.unl.edu.ar.

In angiosperms, the mitochondrial cox2 gene harbors up to two introns, commonly referred to as cox2i373 and cox2i691. We studied the cox2 from 222 fully-sequenced mitogenomes from 30 angiosperm orders and analyzed the evolution of their introns. Unlike cox2i373, cox2i691 shows a distribution among plants that is shaped by frequent intron loss events driven by localized retroprocessing. In addition, cox2i691 exhibits sporadic elongations, frequently in domain IV of introns. Such elongations are poorly related to repeat content and two of them showed the presence of LINE transposons, suggesting that increasing intron size is very likely due to nuclear intracelular DNA transfer followed by incorporation into the mitochondrial DNA. Surprisingly, we found that cox2i691 is erroneously annotated as absent in 30 mitogenomes deposited in public databases. Although each of the cox2 introns is ∼1.5 kb in length, a cox2i691 of 4.2 kb has been reported in Acacia ligulata (Fabaceae). It is still unclear whether its unusual length is due to a trans-splicing arrangement or the loss of functionality of the interrupted cox2. Through analyzing short-read RNA sequencing of Acacia with a multi-step computational strategy, we found that the Acacia cox2 is functional and its long intron is spliced in cis in a very efficient manner despite its length.

UI MeSH Term Description Entries
D007438 Introns Sequences of DNA in the genes that are located between the EXONS. They are transcribed along with the exons but are removed from the primary gene transcript by RNA SPLICING to leave mature RNA. Some introns code for separate genes. Intervening Sequences,Sequences, Intervening,Intervening Sequence,Intron,Sequence, Intervening
D008928 Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive RIBOSOMES, transfer RNAs (RNA, TRANSFER); AMINO ACYL T RNA SYNTHETASES; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs (RNA, MESSENGER). Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. (King & Stansfield, A Dictionary of Genetics, 4th ed) Mitochondrial Contraction,Mitochondrion,Contraction, Mitochondrial,Contractions, Mitochondrial,Mitochondrial Contractions
D001483 Base Sequence The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence. DNA Sequence,Nucleotide Sequence,RNA Sequence,DNA Sequences,Base Sequences,Nucleotide Sequences,RNA Sequences,Sequence, Base,Sequence, DNA,Sequence, Nucleotide,Sequence, RNA,Sequences, Base,Sequences, DNA,Sequences, Nucleotide,Sequences, RNA
D012326 RNA Splicing The ultimate exclusion of nonsense sequences or intervening sequences (introns) before the final RNA transcript is sent to the cytoplasm. RNA, Messenger, Splicing,Splicing, RNA,RNA Splicings,Splicings, RNA
D019684 Magnoliopsida A class of vascular plants which produce flowers and seeds. They include monocotyledons, dicotyledons, and about 80% of all known plant species. Angiosperms,Angiosperma,Angiospermae,Arecidae,Asteridae,Caryophyllidae,Commelinidae,Dicotyledoneae,Dilleniidae,Flowering Plants,Hamamelidae,Hamamelididae,Icacinales,Liliatae,Liliidae,Liliopsida,Magnoliatae,Metteniusales,Oncothecales,Rosidae,Vahliales,Zingiberidae,Angiosperm,Flowering Plant,Icacinale,Metteniusale,Oncothecale,Plant, Flowering,Plants, Flowering,Vahliale

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