Investigation On The Phylogenetics And Evolution History Of Different Lineages In Freshwater Rhodophyta Based On Phylogenomic Analysis

Different lineages of freshwater Rhodophyta were collected and studied.Molecular sequences and organelle genomes were determined and phylogenetic trees were constructed based on different datasets.We analyzed the content and structures of the organelle genomes and inferred the systematics,origin,phylogenetics and evolution of each Rhodophyta lineage.We also identified a new freshwater Rhodophyta species.The results of this study are as follows:1.Three freshwater Rhodophyta representatives including Compsopogon caeruleus,Batrachospermum arcuatum and Thorea hispida were sampled and the complete chloroplast and mitochondrial genomes were determined.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 C.caeruleus.It was inferred that the freshwater members of Rhodophyta occurred through diverse origins based on evidences of genome size,GC content,phylogenomic analysis and divergence time estimation.The freshwater species C.caeruleus and Hildenbrandia rivularis originated and evolved independently at the inland water,whereas the Bangia atropurpurea,Batrachospermum arcuatum and Thorea hispida were derived from the marine relatives.The typical freshwater representatives Thoreales and Batrachospermales were probably derived from the marine relative Palmaria palmata at approximately 415-484 MYA.After the derivation,they evolved independently and partial rearrangement occurred in the chloroplast genomes whereas the mitochondrial genomes remain highly conservative.2.Compsopogon specimens collected in China were examined based on morphology and DNA sequences.Five molecular markers from different genomic compartments including rbc L,COI,18 S rDNA,psbA and UPA were identified and used to construct a phylogenetic relationship.Phylogenetic analyses indicated that two different morphological types from China clustered into an independent clade with Compsopogon specimens when compared to other global samples.The Compsopogon clade with robust support values revealed the affiliation of the samples to C.caeruleus,thus supporting the previous proposal of the monospecific global distribution of this genus.It was speculated that Compsopogon originated in North America,a portion of the Laurentia landmass situated in the Rodinia supercontinent at approximately 573-1701 MYA during the Proterozoic era.Although Compsopogon had evolved for a rather long time,genetic conservation had limited its variability and rate of evolution,resulting in the current monospecific global distribution.We speculated it was caused by the strict habitation demanding and asexual reproduction of this genus.3.Four algal specimens collected in China with morphological resemblance to Audouinella were analyzed,both bluish and reddish thalli included.Molecular phylogenetic analysis was performed to verify the phylogenetic position of these specimens based on three short DNA fragments including psbA,UPA and COI.Phylogenetic relationships based on three DNA fragments were consistent in that the four Audouinella-like thalli clustered together with Thorea hispida with strong support.The four specimens morphologically similar to Audouinella were concluded to represent the chantransia stage of Thoreales based on molecular trees.The reddish specimen shared no sequence divergence with the bluish ones.The three DNA molecular markers demonstrated to be effective to ascertain the phylogenetic position of acrochaetioid algae specimens,and to delineate other freshwater Rhodophyta.4.Batrachospermum specimens collected in China were investigated using molecular biological methods.Phylogenetic trees based on psaA,psbA and UPA sequences were supported robustly.It showed sections Hybrida and Contorta previously belonging to genus Batrachospermum clustered together and separated from other specimens of this genus.The proposal of a new genus Kumanoa constituting of sections Hybrida and Contorta was supported in this study.Additionally,B.gelatinosum was separated with other Batrachospermum species including B.hongdongense,B.longipedicellatum and B.arcuatum.Therefore the new genus Sheathia was supported and only one species B.gelatinosum belonged to section Batrachospermum.5.Freshwater Hildenbrandia specimens were collected from Jigongshan Mountain,China.Morphological and molecular analysis were conducted on the specimens.Morphological observation showed this specimen distinguished from the other freshwater Hildenbrandia members by significantly larger cell dimensions(9.8-19.6)?(9.9-10.4)?m and filament height(364-409 ?m).Phylogenetic analysis based on rbcL gene sequences showed the specimens formed a clade divergent from H.rivularis group with robust support values and was in the basal position.Secondary structures based on 18 S rRNA sequences distinguished the new species by absence of 3 helices compared with common structure of H.rivularis.Combining the morphological and molecular evidence,a new freshwater red alga,Hildenbrandia jigongshanensis F.Nan & S.Xie was proposed.This new species was distinguished from the other freshwater members by significantly larger cell dimensions and filament height.As an important constituent in freshwater flora,the freshwater Rhodophyta was anciently derived and performed invaluable function in the plant evolution.With the decrease of freshwater resources and increased water pollution,the survival of freshwater Rhodophyta is threatened severelly.Therefore,it is essential to conduct further investigation on this rare and fragile taxa.It can provide robust support for the photosynthesis investigation and biodiversity conservation.