Origin of minicircular mitochondrial genomes in red algae

Abstract

Eukaryotic organelle genomes are generally of conserved size and gene content within phylogenetic groups. However, significant variation in genome structure may occur. Here, we report that the Stylonematophyceae red algae contain multipartite circular mitochondrial genomes (i.e., minicircles) which encode one or two genes bounded by a specific cassette and a conserved constant region. These minicircles are visualized using fluorescence microscope and scanning electron microscope, proving the circularity. Mitochondrial gene sets are reduced in these highly divergent mitogenomes. Newly generated chromosome-level nuclear genome assembly of Rhodosorus marinus reveals that most mitochondrial ribosomal subunit genes are transferred to the nuclear genome. Hetero-concatemers that resulted from recombination between minicircles and unique gene inventory that is responsible for mitochondrial genome stability may explain how the transition from typical mitochondrial genome to minicircles occurs. Our results offer inspiration on minicircular organelle genome formation and highlight an extreme case of mitochondrial gene inventory reduction.

Complete Mitogenome Sequencing, Annotation, and Phylogeny of Grateloupia turuturu, a Red Alga with Intronic cox1 Gene

“…Similar outcomes have been documented for all G. angusta, G. cornea, G. elliptica, G. filicina, and G. taiwanensis , but not for P. affinis and P. lancifolius ( Table 1 ) [ 6 , 7 , 8 , 9 , 10 , 11 ]. Group II intronic cox1 and trnI are the unique features of red algal mitogenomes [ 12 , 13 , 15 ]. The ymf39 gene is transcribed between cox3 and trnG genes in the mitogenome of G. turuturu and encodes an ATP synthase B chain precursor.…”

“…Relatively little is known about the mitogenome of Rhodophytes, and due to advancements in software and molecular technologies, more and more detailed studies are being reported. In fact, red algal mitogenomes are more complete than previously reported [ 12 ], and it has also been reported that red algae, Strylonematophyceae , contain multiple minicircular mitochondrial genomes that encode one or two genes [ 13 ]. These studies are made possible by applying bundles of software tools.…”

Evolution and maintenance of mtDNA gene content across eukaryotes

“…Minicircles, almost corresponding to individual mtDNA genes, have been recently reported in red algae (Y. Lee et al, 2023). The euglenozoan Diplonema papillatum has multiple small mtDNA fragments smaller than the size of individual genes, which must be spliced together from these fragments (Vlcek et al, 2011).…”