Research Article |
Corresponding author: Shulian Xie ( xiesl@sxu.edu.cn ) Academic editor: Juliet Brodie
© 2022 Jinfen Han, Fangru Nan, Jia Feng, Junping Lv, Qi Liu, Xudong Liu, Shulian Xie.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Han J, Nan F, Feng J, Lv J, Liu Q, Liu X, Xie S (2022) Thorea baiyunensis sp. nov. (Thoreales, Rhodophyta) and T. okadae, a new record from China. PhytoKeys 193: 107-123. https://doi.org/10.3897/phytokeys.193.79667
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The freshwater red algal order Thoreales has a triphasic life history, of which the “Chantransia” phase is a small filamentous sporophyte. The “Chantransia” stage is difficult to distinguish from species in the genus Audouinella by its morphological characteristics. In this study, five “Chantransia” isolates (GX41, GX81, GD224, GD225, GD228) were collected from Guangxi Zhuang Autonomous Region and Guangdong Province in China. Based on morphological data, all five isolates were similar to A. pygmaea, whereas sequence data from the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene and the 5’ region of the mitochondrial cytochrome oxidase I gene (COI-5P) determined that these specimens represented the “Chantransia” stage of two species in the genus Thorea rather than Audouinella. Phylogenetic analyses of the concatenated genes supported the proposal of a new species, T. baiyunensis, and a new geographic record of T. okadae, a species previously described only in Japan. Therefore, combined with previous records, four species of this genus are now recognized in China, including T. hispida, T. violacea, T. baiyunensis and T. okadae.
COI-5P, freshwater Rhodophyta, new taxon, phylogeny, rbcL, Thorea
Currently, more than 7,000 red algal species are reported worldwide, of which freshwater species only account for 3%. In the Rhodophyta, only four orders (Balbianiales, Batrachospermales, Compsopogonales, and Thoreales) have all members that are strictly freshwater species. Among the freshwater red algae, the genus Thorea Bory was established by
As currently recognized, the Thoreales contain a single family Thoreaceae with two genera, Thorea and Nemalionopsis. The main difference between the genera Thorea and Nemalionopsis is that Thorea has assimilatory filaments that are not contained in a common gelatinous matrix with reproductive structures (carpogonia, spermatangia, carposporangia and monosporangia) at their base and a lower ratio of sporangial branch to assimilatory filament length and loose aggregation (
Like other sexually reproductive species of freshwater red algae, Thorea species have a triphasic life history, including gametophyte, carposporophyte, and a diminutive diploid sporophyte termed “Chantransia” stage. Recently, several studies have focused on the phylogenetic affinities of the “Chantransia” stages of Thorea and the relationship between the isolates in this stage and a phylogenetically distant genus Audouinella Bory (
It is therefore evident that the morphological difference between “Chantransia” stages and Audouinella is not clear. Relying solely on traditional morphological methods can often cause confusion in the classification and identification of Audouinella-like freshwater red algae. All samples in this study are “Chantransia” stages, meaning that key diagnostic morphological characters were unavailable. Therefore, the present work has attempted to use two molecular markers (rbcL and COI-5P) to infer the phylogenetic position of all isolates in this study. In addition, a secondary aim of this investigation is to provide reference for local resource survey of freshwater red algae biodiversity in China.
Five “Chantransia” specimens (GX41, GX81, GD224, GD225 and GD228) were collected from Guangxi Zhuang Autonomous Region and Guangdong Province in China (Fig.
Collection information and sequence accession numbers for taxa analyzed in this study.
Isolate | Locality with longitude and latitude | Collection date | Collector | Voucher number |
---|---|---|---|---|
GX41 | Baimo Cave, Bama County, Guangxi Zhuang Autonomous Region, China (24°18.03'N, 107°05.96'E) | 22 December 2019 | Kunpeng Fang | GX19041 |
GX81 | Tongling Great Falls, Jinxi County, Guangxi Zhuang Autonomous Region, China (23°43.10'N, 106°39.77'E) | 23 December 2019 | Kunpeng Fang | GX19081 |
GD224 | Baiyun Mountain, Guangzhou, Guangdong province, China (23°36.00'N, 113°49.53'E) | 22 November 2020 | Jinfen Han and Kunpeng Fang | GD20224 |
GD225 | Baiyun Mountain, Guangzhou, Guangdong province, China (23°36.00'N, 113°49.53'E) | 22 November 2020 | Jinfen Han and Kunpeng Fang | GD20225 |
GD228 | Baiyun Mountain, Guangzhou, Guangdong province, China (23°36.00'N, 113°49.53'E) | 22 November 2020 | Jinfen Han and Kunpeng Fang | GD20228 |
Total DNA was extracted following the protocol originally described by
GenBank accession numbers of rbcL and COI-5P sequences generated in this study.
The rbcL data matrix included 56 specimens of Thoreales and 2 outgroup taxa, consisting of 1203 characters, of which 410 (34.08%) were variable and 380 (31.59%) were parsimony informative. The rbcL p-distance among the five “Chantransia” isolates and other specimens of order Thoreales (Suppl. material
The COI-5P sequence determined for the five “Chantransia” isolates from this study were 676 bp, of which 297 (43.93%) were variable and 273 (40.38%) were parsimony informative. The pairwise distance among the “Chantransia” isolates collected in this study and other Thoreales taxa (Suppl. material
Phylogenetic analyses based on single gene and concatenated genes produced trees with similar tree topologies, such that only the concatenated B.I. tree with supporting values calculated from two methods was displayed (Fig.
Bayesian inference tree for Thorea and Nemalionopsis based on concatenated sequences from rbcL and COI-5P genes. Support values for all analyses are shown as follows: Bayesian posterior probabilities/ML bootstrap. ‘-’ denotes <50% support for those analyses at that node. All new sequences generated in this study are indicated in red boxes.
The phylogenetic analyses strongly supported the monophyly of the Thoreales, Nemalionopsis and Thorea (Fig.
The morphometric data showed that all samples used in this study fit the morphological description of Audouinella pygmaea (Roth) Duby, although the tuft length of GX81 is significantly smaller than others (Fig.
Thalli characteristics | GX41 | GX81 | GD224 | GD225 | GD228 |
---|---|---|---|---|---|
Color | Bluish | Brownish | Bluish | Bluish | Bluish |
Height (mm) | (4.8) 5–9.4 (10.0) | (1.2) 1.5–3.5 (4.4) | (3.4) 4.1–9.3 (10.8) | (4.1) 5.4–22.9 (25.9) | (8.5) 8.8–12.9 (13.6) |
Branch angle* | ≤ 25° | < 25° | < 25° | < 25° | < 25° |
Vegetative cells Length (μm) | (8.2) 10–28.2 (31.8) | (20.9) 22.7–54.5 (59.1) | (12.7) 13.6–63.6 (68.2) | (21.8) 22.7–59.1(60.9) | (22.7) 23.6–43.6 (45.5) |
Vegetative cells Diameter (μm) | (7.2) 8.2–10.9 (11.8) | (8.2) 9.1–10.9 (11.8) | (8.2) 10.9–15.5 (16.4) |
(10.9) 11.8–15.5 (16.4) |
(11.8) 12.7–20.9 (22.7) |
Monosporangia Shape | Obovoidal | Obovoidal | Obovoidal | Obovoidal | Obovoidal |
Monosporangia Length (μm) | (12.7) 13.6–14.5 (15.5) | (12.7) 13.6–18.2 (19.1) | (11.8) 12.7–21.8 (22.7) |
(12.7) 13.6–17.3 (19.1) |
(13.6) 14.5–21.8 (23.6) |
Monosporangia Diameter (μm) | (7.2) 8.2–14.5 (15.5) | (8.2) 9.1–12.7 (13.6) | (10.9) 11.8–15.5 (16.4) |
(10.9) 11.8–13.6 (14.5) |
(10.9) 11.8–16.4 (17.3) |
Chloroplast number | 2–4 | 2–4 | 2–4 | 2–4 | 2–4 |
Chloroplast shape | laminate or irregularly lobed | laminate or irregularly lobed | laminate or irregularly lobed | laminate or irregularly lobed | laminate or irregularly lobed |
Morphological characters of samples investigated in this study A–D sample GX41 A morphological observation of the tufts of erect filament, bluish in color B monosporangial branch with ovoid monosporangium (black arrow) C filament showing branch angle ≤ 25° (black arrow) D erect filaments arise from basal system consisting of a prostrate mass with sparse rhizoids (black arrowhead) E–H sample GX81 E morphological observation of the tufts of erect filament, brownish in color F monosporangial branch with ovoid monosporangium (black arrow) G filament showing branch angle < 25° (black arrow) H cells have parietal laminate or irregularly lobed Chloroplast (white arrow) I–L sample GD224 I morphological observation of the tufts of erect filament, bluish in color J monosporangial branch with obovoidal monosporangium (black arrow) K filament showing branch angle < 25° (black arrow) L cells have parietal laminate or irregularly lobed Chloroplast (white arrow) M–O sample GD225 M morphological observation of the tufts of erect filament, bluish in color N monosporangial branch with obovoidal monosporangium (black arrow) O filament showing branch angle < 25° (black arrow) P cells have parietal laminate or irregularly lobed Chloroplast (white arrow) Q–T sample GD228 Q morphological observation of the tufts of erect filament, bluish in color R monosporangial branch with obovoidal monosporangium (black arrow) S filament showing branch angle < 25° (black arrow) T cells have parietal laminate or irregularly lobed Chloroplast (white arrow).
The genetic distance and phylogenetic analysis based on rbcL, COI-5P and the concatenated genes all supported the identification of new species described below.
Known only from the “Chantransia” sporophyte generation. Plant macroscopic, up to 25.9 mm, bluish; basal portion consisting of an irregular prostrate system of densely aggregated filaments; lateral branches developing at angle < 25°. Vegetative cells of main branches cylindrical, (12.7) 13.6–63.6 (68.2) μm long and (8.2) 10.9–20.9 (22.7) μm in diameter. Monosporangia numerous, mostly grow at the tip of 1–5-celled, short branchlets, singly or in clusters, obovoidal, (11.8) 12.7–21.8 (23.6) μm long and (10.9) 11.8–16.4 (17.3) μm in diameter. Chloroplasts laminate or irregularly lobed, 2–4 per cell.
China, Guangdong Province, Baiyun Mountain, 540 m alt., 23°36.00'N, 113°49.53'E: epilithic on the rocks in spring water, November 2020, J.F. Han & K.P Fang (Holotype: SXU-SAS18040; Paratype: SXU-SAS18041). Deposited in Herbarium of Shanxi University (SXU), Shanxi University, Taiyuan, Shanxi Province, China.
The species epithet refers to the type locality (Baiyun Mountain, China).
SXU-GD20224.
Several studies have confirmed that it is difficult to distinguish “Chantransia” stages from true Audouinella based only on morphological characteristics, which often hinders species identification and brings confusion to the classification system of freshwater red algae (
With the widespread application of molecular data in the taxonomy of freshwater red algae, the view that morphologically simple organisms have considerable genetic diversity and species richness has been widely recognized (
In 1949, Yamada reported a new species, T. okadae, when studying the specimens of genus Thorea in Kagoshima prefecture, Japan (
In a study on the seasonality of gametophyte occurrence, maturation and fertilization of the freshwater red alga T. okadae,
We are grateful to the National Natural Science Foundation of China (41871037, 31800172, and 32170204) and the Fund for Shanxi “1331 Project”.
Figure S1
Data type: COL
Explanation note: Bayesian inference tree based on the rbcL gene sequences. Support values for all analyses are shown as follows: Bayesian posterior probabilities/ML bootstrap. ‘-’ denotes <50% support for that analysesat that node. All new sequences generated in this study are indicated in red boxes.
Figure S2
Data type: COL
Explanation note: Bayesian inference tree based on the COI-5P gene sequences. Support values for all analyses are shown as follows: Bayesian posterior probabilities/ML bootstrap. ‘-’ denotes <50% support for that analyses at that node. All new sequences generated in this study are indicated in red boxes.
Table S1
Data type: docx
Explanation note: Specimen information of sequences downloaded from the GenBank database. “–” denotes no related information for the specimen.
Table S2
Data type: xls
Explanation note: Pairwise distance (lower-left matrix) and number of nucleotide variance (upper-right matrix) of rbcL sequence among the taxa in this study.
Table S3
Data type: xls
Explanation note: Pairwise distance (lower-left matrix) and number of nucleotide variance (upper-right matrix) of COI-5P sequence among the taxa in this study.