Complete mitochondrial genomes of six species of the freshwater red algal order Batrachospermales (Rhodophyta)

Orlando Necchi,Joana F Costa,Olivier De Clerck,Shao-Lun Liu,Monica O Paiano,Heroen Verbruggen,Andrea Del Cortona

doi:10.1080/23802359.2018.1473734

Abstract

Only two mitochondrial (mt) genomes had been reported in members of the red algal order Batrachospermales, which are confined to freshwater habitats. Additional mt genomes of six representative members (Batrachospermum macrosporum, Kumanoa ambigua, K. mahlacensis, Paralemanea sp., Sheathia arcuata, and Sirodotia delicatula) were sequenced aiming to gain insights on the evolution of their mt genomes from a comparative analysis with other red algal groups. Mt genomes sequenced had the following characteristics: lengths ranging between 24,864 nt and 29,785 nt, 22 to 26 protein-coding genes, G + C contents of 21.3 to 30.7%, number of tRNA of 16 to 37, non-coding DNA from 3.8% to 14.8%. Comparative analysis revealed that mt genomes in Batrachospermales are highly conserved in terms of genome size and gene content and synteny. Phylogenetic analyses based on COI nucleotide data revealed high bootstrap support only for the genera usually recovered in the phylogenetic analyses but no support for supra-generic groups. The insertion of a group II intron carrying an ORF coding for the corresponding intron maturase interrupting the COI gene was observed in Paralamenea sp. and accounted for its larger genome in comparison to the other Batrachospermales mt genomes.

Highlights

The red algae (Rhodophyta) consists of a diverse group of photosynthetic eukaryotes, most inhabiting marine environments (98%), but many restricted to freshwater habitats (Gurgel and Lopez-Bautista 2007)
All the sequenced Batrachospermales mt genomes mapped as circular molecules (Supplementary Figures 1–3) and their lengths ranged from 24,864 nt (B. macrosporum) to 29,785 nt (Paralemanea sp.)
The G þ C contents varied between 21.3% (K. mahlacensis) and 30.7% (S. delicatula.) and non-coding DNA ranged from 3.8% (S. delicatula) to 14.8% (K. ambigua) of the assembled genomes (Table 1)

Summary

Introduction

The red algae (Rhodophyta) consists of a diverse group (around 7150 species) of photosynthetic eukaryotes, most inhabiting marine environments (98%), but many restricted to freshwater habitats (Gurgel and Lopez-Bautista 2007). Subclass Nemaliophycidae is the only orders with exclusively freshwater members (Balbianiales, Batrachospermales, and Thoreales). Batrachospermales is the most diverse in terms of morphology, reproductive characters, and number of taxa among the freshwater red algal orders (Kumano 2002; Entwisle et al 2009; Lam et al 2015). Members of Batrachospermales are characterized by the following combination of features (Pueschel and Cole 1982; Garbary and Gabrielson 1990; Kumano 2002; Entwisle et al 2009): heterotrichous, uniaxial, gelatinous or cartilaginous plants; axial cells having determinant lateral assimilatory filaments; pit plugs with two cap layers and with an expanded dome-shaped outer layer; absence of tetraspores and meiosis taking place in diploid vegetative cells giving rise to haploid axes; multiple discoid chloroplasts without pyrenoids; exclusively freshwater occurrence

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Results