Origin and evolutionary history of freshwater Rhodophyta: further insights based on phylogenomic evidence

Fangru Nan,Kunpeng Fang,Shulian Xie,Jia Feng,Chaoyan Gong,Junping Lv,Qi Liu

doi:10.1038/s41598-017-03235-5

Abstract

Freshwater representatives of Rhodophyta were sampled and the complete chloroplast and mitochondrial genomes were determined. Characteristics of the chloroplast and mitochondrial genomes were analyzed and phylogenetic relationship of marine and freshwater Rhodophyta were reconstructed based on the organelle genomes. The freshwater member Compsopogon caeruleus was determined for the largest chloroplast genome among multicellular Rhodophyta up to now. Expansion and subsequent reduction of both the genome size and GC content were observed in the Rhodophyta except for the freshwater Compsopogon caeruleus. It was inferred that the freshwater members of Rhodophyta occurred through diverse origins based on evidence of genome size, GC-content, phylogenomic analysis and divergence time estimation. The freshwater species Compsopogon caeruleus and Hildenbrandia rivularis originated and evolved independently at the inland water, whereas the Bangia atropurpurea, Batrachospermum arcuatum and Thorea hispida are derived from the marine relatives. The typical freshwater representatives Thoreales and Batrachospermales are probably derived from the marine relative Palmaria palmata at approximately 415–484 MYA. The origin and evolutionary history of freshwater Rhodophyta needs to be testified with more organelle genome sequences and wider global sampling.

Highlights

Rhodophyta is an anciently derived lineage, constituting one of the primary plastids-bearing hosts, and provides plastids for the secondary or tertiary endosymbiosis[1]
We proposed a primary inference on the origin and evolutionary history of freshwater Rhodophyta, which needs to be testified with more sequence data and wider sampling
Of all the reported complete chloroplast genomes of multi-cellular freshwater Rhodophyta, Compsopogon caeruleus owned the largest genome size, and the chloroplast genome of Batrachospermum arcuatum and Thorea hispida were in the range of Florideophyceae[9, 12, 16, 17]

Summary

Introduction

Rhodophyta is an anciently derived lineage, constituting one of the primary plastids-bearing hosts, and provides plastids for the secondary or tertiary endosymbiosis[1]. Red algae in freshwater habitats tend to be macroscopic and benthic, exhibiting a smaller size range than the marine members[6] Their morphology varied from unicellular to multicellular forms including tufts, crusts and filaments. Chloroplast genomes of the red algae have high gene capacity and compact structure[8, 9], and the mitochondria genomes of Florideophyceae are highly conserved despite a wide variety of morphological divergence[10]. We proposed a primary inference on the origin and evolutionary history of freshwater Rhodophyta, which needs to be testified with more sequence data and wider sampling

Methods

Results

Conclusion