The Rhodoexplorer Platform for Red Algal Genomics and Whole-Genome Assemblies for Several Gracilaria Species.

Macroalgal (seaweed) genomic resources are generally lacking as compared with other eukaryotic taxa, and this is particularly true in the red algae (Rhodophyta). Understanding red algal genomes is critical to understanding eukaryotic evolution given that red algal genes are spread across eukaryotic lineages from secondary endosymbiosis and red algae diverged early in the Archaeplastids. The Gracilariales is a highly diverse and widely distributed order including species that can serve as ecosystem engineers in intertidal habitats and several notorious introduced species. The genus Gracilaria is cultivated worldwide, in part for its production of agar and other bioactive compounds with downstream pharmaceutical and industrial applications. This genus is also emerging as a model for algal evolutionary ecology. Here, we report new whole-genome assemblies for two species (Gracilaria chilensis and Gracilaria gracilis), a draft genome assembly of Gracilaria caudata, and genome annotation of the previously published Gracilaria vermiculophylla genome. To facilitate accessibility and comparative analysis, we integrated these data in a newly created web-based portal dedicated to red algal genomics (https://rhodoexplorer.sb-roscoff.fr). These genomes will provide a resource for understanding algal biology and, more broadly, eukaryotic evolution.

Phylogeography of the red alga Gracilariopsis tenuifrons (Gracilariales) along the Brazilian coast.

Changes in the sea level during the Holocene are regarded as one of the most prevalent drivers of the diversity and distribution of macroalgae in Brazil, influenced by the emergence of the Vitória-Trindade seamount chain (VTC). Gracilariopsis tenuifrons has a wide geographic distribution along the Brazilian coast, from Maranhão state (2°48'64.3" S) to Santa Catarina state (27.5°73'83" S). The knowledge of historical processes affecting diversity may allow the development of conservation strategies in environments against anthropogenic influence. Therefore, knowledge about phylogeography and populational genetic diversity in G. tenuifrons is necessary. Six populations were sampled along the northeastern tropical (Maranhão-MA, Rio Grande do Norte-RN, Alagoas-AL, and Bahia-BA States) and southeastern subtropical (São Paulo "Ubatuba"-SP1 and São Paulo "Itanhaém"-SP2 States) regions along the Brazilian coast. The genetic diversity and structure of G. tenuifrons were inferred using mitochondrial (COI-5P and cox2-3 concatenated) DNA markers. Gracilariopsis tenuifrons populations showed an evident separation between the northeast (from 2°48'64.3" S to 14°18'23" S; 17 haplotypes) and the southeast (from 23°50'14.9" S to 24°20'04.7" S; 10 haplotypes) regions by two mutational steps between them. The main biogeographical barrier to gene flow is located nearby the VTC. The southeast region (São Paulo State) is separated by two subphylogroups (SP1, three haplotypes and SP2, six haplotypes), and Santos Bay (estuary) has been considered a biogeographical barrier between them. The presence of genetic structure and putative barriers to gene flow are in concordance with previous studies reporting biogeographic breaks in the southwest Atlantic Ocean, including the genetic isolation between northeast and southeast regions for red and brown algae in the vicinity of the VTC.

Dual influence of terrestrial and marine historical processes on the phylogeography of the Brazilian intertidal red alga Gracilaria caudata.

In this study, we explored how past terrestrial and marine climate changes have interacted to shape the phylogeographic patterns of the intertidal red seaweed Gracilaria caudata, an economically important species exploited for agar production in the Brazilian north-east. Seven sites were sampled along the north-east tropical and south-east sub-tropical Brazilian coast. The genetic diversity and structure of G. caudata was inferred using a combination of mitochondrial (COI and cox2-3), chloroplast (rbcL) and 15 nuclear microsatellite markers. A remarkable congruence between nuclear, mitochondrial and chloroplast data revealed clear separation between the north-east (from 03° S to 08° S) and the south-east (from 20° S to 23° S) coast of Brazil. These two clades differ in their demographic histories, with signatures of recent demographic expansions in the north-east and divergent populations in the south-east, suggesting the maintenance of several refugia during the last glacial maximum due to sea-level rise and fall. The Bahia region (around 12° S) occupies an intermediate position between both clades. Microsatellites and mtDNA markers showed additional levels of genetic structure within each sampled site located south of Bahia. The separation between the two main groups in G. caudata is likely recent, probably occurring during the Quaternary glacial cycles. The genetic breaks are concordant with (i) those separating terrestrial refugia, (ii) major river outflows and (iii) frontiers between tropical and subtropical regions. Taken together with previously published eco-physiological studies that showed differences in the physiological performance of the strains from distinct locations, these results suggest that the divergent clades in G. caudata correspond to distinct ecotypes in the process of incipient speciation and thus should be considered for the management policy of this commercially important species.

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales, Rhodophyta) under solar UV radiation.

The effects of solar UV radiation on mycosporine-like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.

The effects of NO3(-) supply on Mazzaella laminarioides (Rhodophyta, Gigartinales) from southern Chile.

The effects of nitrate supply on growth, pigments, mycosporine-like amino acids (MAAs), C:N ratios and carrageenan yield were investigated in Mazzaella laminarioides cultivated under solar radiation. This species is economically important in southern Chile where an increase of nitrogen in coastal waters is expected as a consequence of salmon aquaculture activity. Apical segments were cultivated in enriched seawater with five different NO3(-) concentrations (0, 0.09, 0.18, 0.38 and 0.75 mm) during 18 days. Although phycoerythrin and phycocyanin content, as well as C:N ratios, were reduced in the control treatment (without NO3(-) supply), when compared to NO3(-) treatments, total MAA concentration, carrageenan yield and growth rates were similar in all tested conditions. Nevertheless, during the experiment, an important synthesis of mycosporine-glycine took place in a nitrate concentration-dependent manner, with accumulation being saturated around 0.18 mm of nitrate. These results indicate that exposure to high NO3(-) concentration of more than 100 times the values observed in the nature did not impair the photoprotection system, as determined by MAAs, nor did it have a deleterious effect on growth or carrageenan yield of M. laminarioides, a late successional species from Chile.

Phenology of an agarophyte Gracilaria birdiae Plastino and E.C. Oliveira (Gracilariales, Rhodophyta) in Northeastern Brazil

The reproductive phenology and thallus length of Gracilaria birdiae were studied over a period of 12 months in a natural bed in Northeastern Brazil. Fertile specimens of G. birdiae were observed during the entire study period. Tetrasporophytes were the most common with an annual mean of 80.1±5.6 percent, followed by cystocarpic plants (9.3±3.4 percent), male gametophytes (8.3±3.6 percent) and infertile plants (2.2±3.4 percent). Only male gametophytes and infertile plants showed a variation in occurrence frequency during the year (p<0.05). With respect to thallus length, a distinct seasonal variation was observed for all reproductive stages (p<0.05), with the highest values recorded during the rainy season (March to August) and the lowest in the dry season (September to February). The results demonstrate that the size of individuals in this population is significantly affected by the periodic changes in the environment caused by rainfall regimes and hydrodynamism.

UVB radiation induces changes in the ultra-structure of Iridaea cordata.

Iridaea cordata cultivated in the presence of UVB radiation (UVBR) was studied using transmission electron microscopy. Apical segments were cultivated in 0.97Wm(-2) of UVBR for 40 days, 3h a day, and compared to a negative control (UVBR absent). UVBR caused modifications, mainly in the cortical cells, including an increased number of cell wall-producing vesicles, in addition to thicker and denser cellular walls, compared to the control. Additionally, cells were observed with an irregular contour and without defined organelles. The increase of cell-wall thickness could be interpreted as an acclimation to UVBR, which could lead to protection from this radiation.