Abstract
Sargassum is one of the most important genera of the family Sargassaceae in brown algae and is used to produce carrageenan, mannitol, iodine, and other economic substances. Here, seven complete plastid genomes of Sargassum ilicifolium var. conduplicatum, S. graminifolium, S. phyllocystum, S. muticum, S. feldmannii, S. mcclurei, and S. henslowianum were assembled using next-generation sequencing. The sizes of the seven circular genomes ranged from 124,258 to 124,563 bp, with two inverted regions and the same set of plastid genes, including 139 protein-coding genes (PCGs), 28 transfer (t)RNAs, and 6 ribosomal (r)RNAs. Compared with the other five available plastid genomes of Fucales, 136 PCGs were conserved, with two common ones shared with Coccophora langsdorfii, and one with S. fusiforme and S. horneri. The co-linear analysis identified two inversions of trnC(gca) and trnN(gtt) in ten Sargassum species, against S. horneri and C. langsdorfii. The phylogenetic analysis based on the plastid genomes of 55 brown algae (Phaeophyceae) showed four clades, whose ancient ancestor lived around 201.42 million years ago (Mya), and the internal evolutionary branches in Fucales started to be formed 92.52 Mya, while Sargassum species were divided into two subclades 14.33 Mya. Our novel plastid genomes provided evidence for the speciation of brown algae and plastid genomic evolution events.
Highlights
The brown algal genus Sargassum, which belongs to the Class Phaeophyceae, Subclass Fucophycidae, Order Fucales, Family Sargassaceae, contains 360 species,1 accounting for 65% of the Fucales (Guiry and Guiry, 2021)
The plastid genome contains a typical pair of inverted repeat (IR) regions (Henry, 2005), which are often observed in the plastid genomes of advanced plants and green algae (Cao, 2015)
The expansion and contraction of IR regions in the plant plastid genome is a common phenomenon that contributes to the plant plastid genome size (Huang et al, 2014)
Summary
The brown algal genus Sargassum, which belongs to the Class Phaeophyceae, Subclass Fucophycidae, Order Fucales, Family Sargassaceae, contains 360 species, accounting for 65% of the Fucales (Guiry and Guiry, 2021). As a supplier of marine primary productivity, provides habitats, breeding grounds, and food sources for a variety of marine creatures (Godoy and Ricardo, 2002), and improves the ecological environment of the shallow sea (Komatsu et al, 2007; Williams and Feagin, 2010). The various nutrient contents extracted from Sargassum, such as polysaccharides, are of high economic value for food, health, and medicine (Sousa et al, 2007; Ermakova et al, 2011; Liu et al, 2012). Many studies on Sargassum have been conducted on culture techniques (Hales and Fletcher, 1990; Aaron-Amper et al, 2020), genetic diversity (Engelen et al, 2001; Cheang et al, 2010b; Sarkar et al, 2015), and phylogenetic analysis (Sung Mi Cho et al, 2012; Dixon et al, 2014; Liu et al, 2016)
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