Mitochondrial genome sequences uncover evolutionary relationships of two Sargassum subgenera, Bactrophycus and Sargassum

Abstract

To elucidate the evolution of mitochondrial genomic diversity between two Sargassum subgenera, Bactrophycus and Sargassum, we sequenced four Sargassum genomes in subgenus Sargassum, including Sargassum polycystum C. Agardh, S. spinuligerum Sonder, S. ilicifolium (Turner) C. Agardh, and S. aquifolium (Turner) C. Agardh. Mitogenome sizes of these four species ranging from 34,761 to 34,925 bp are longer than those in subgenus Bactrophycus (34,606 to 34,748 bp), and the content of non-coding regions (4.68–5.25%) is higher than that in Bactrophycus (4.29–4.65%). The evolutionary traits of single mitochondrial genes show apparent inconsistency between the two Sargassum subgenera. Mitogenome sequence identities are from 92.4 to 99.1% in subgenus Sargassum and from 87.6 to 92.7% in subgenus Bactrophycus. Based on the whole mitogenome dataset, ten Sargassum species are clustered into two subclades representing two subgenera, Sargassum and Bactrophycus. Only four individual single-gene phylogenies (cox2, nad6, rpl5, and rps3) show that the ten Sargassum species could be strongly clustered and divided into two subgenera with high values (ML/NJ/BI ≥70%). The study indicates that the two subgenera, Sargassum and Bactrophycus, are distinct evolutionary entities, and mitogenomic traits provide novel insights into Sargassum deep-level relationships.