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. 2017 Sep 11;2(2):656–657. doi: 10.1080/23802359.2017.1375877

The complete mitogenome of ‘Zaohoucheng’, an important Saccharina japonica cultivar in China

Jing Zhang a,✉, Nan Li a, Na Liu b, Tao Liu b,✉
PMCID: PMC7800536  PMID: 33473936

Abstract

Saccharina japonica is one of the most important economic seaweeds. Here, complete mitogenome of S. japonica cultivar ‘Zaohoucheng’ were reported. Its circular mapping organization with the length of 37,657 bp had an overall A + T content of 64.70% and encoded three rRNAs, 25 tRNAs, 35 known mitochondrial proteins and three ORFs. From the total alignment of S. japonica and its cultivar ‘Zaohoucheng’, only 12 nucleotide substitutions were detected. Gene arrangement and component of ‘Zaohoucheng’ mitogenome were identical to those of reported Saccharina species, indicating highly conservative evolution. The phylogenetic analysis showed that ‘Zaohoucheng’ had a closer relationship with S. japonica which strongly supported the parental origin of 'Zaohoucheng'.

Keywords: Cultivar, 'Zaohoucheng', conservative evolution, mitogenome, parental origin, phylogenetic relationship

Saccharina japonica (Laminariales, Phaeophyceae) is one of the most important seaweeds due to its economic value and global distribution (Kain 1979). About 20 cultivars have been bred (Zhang et al. 2016a) in China and ‘Zaohoucheng’ is an important inbred line of S. japonica mainly cultured in North China. Here, we determined its complete mitogenome, gave the comparison with that of S. japonica and conducted phylogenetic analysis to reveal the genetic and evolutionary characteristics at genomic level.

One ‘Zaohoucheng’ sample (specimen number: 2010084028) was collected from Lidao Bay, Shandong, China (37°13′N, 122°34′E) and stored at −80 °C for DNA extraction. The experimental scheme and data processing were followed by the previous report (Zhang et al. 2011).

Complete mitogenome of ‘Zaohoucheng’ was characterized as a circular molecule with the length of 37,657 bp (GenBank accession no. KX073816). Its mitogenome had an overall AT content of 64.70% exhibiting a high AT richness. Cumulative AT-skew (–0.1218) and GC-skew (0.1660) analysis reflected a light bias toward T and G on H-strand. The mitogenome encoded 66 genes, including three rRNAs (23S, 16S and 5S), 25 tRNAs, 35 protein-encoding genes and three ORFs. With the exception of rpl2, rpl16, rps3, rps19, tatC and ORF130, 60 genes were encoded on H-strand. The protein-encoding regions were 29,007 bp in length. One conserved gene cluster (rps8–rpl6–rps2–rps4) was also found. All protein-encoding genes started with ATG codon and 68.42% terminated with TAA codon, higher than that for TAG (21.05%) and TGA (10.53%).

From the total alignment of S. japonica and ‘Zaohoucheng’, 12 nucleotide substitutions were detected which six led to the variety of amino acid. No substitutions were observed in tRNA genes. In conclusion, the component and arrangement of mitogenome were consistent with those of reported Saccharina species and cultivars (Yotsukura et al. 2010; Zhang et al. 2011, 2013, 2016b, 2016c), showing highly conservative evolution.

Bayesian analysis based on the whole mitogenome sequences shared by 16 available Laminariaceae algae was utilized to reconstruct the phylogeny. Ectocarpus siliculosus as outgroup. Species were divided into two groups: Saccharina and Laminaria supporting existing taxonomic systems (Yoon et al. 2001; Lane et al. 2006), and all reported cultivars in China were in Saccharina clade (Figure 1). Additionally, ‘Zaohoucheng’ first groups with S. japonica which validated its parental origin.

Figure 1.

Figure 1.

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Phylogenetic tree constructed based on combined 35 mtDNA protein-encoding genes using Bayesian analysis.

Disclosure statement

There are no conflicts of interest for all the authors including the implementation of research experiments and writing this article.

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