Phylogenetic relationships in the genera Zostera and Heterozostera (Zosteraceae) based on matK sequence data

Anti-phototoxicity and anti-melanogenesis activities of eelgrass Zostera marina and its phenolic constituents

The eelgrass Zostera marina L. has several economic roles, from its earlier usage in the insulation industry to protecting the earth from global warming. In this study, we aimed to discover the cosmetic potential of Z. marina. A methanolic extract of Z. marina showed anti-phototoxicity and anti-melanogenesis activity with an IC50 of 17.5 μM, followed by a phytochemical analysis of its phenolic constituents. Ten compounds (1-10) were isolated by several chromatographic techniques and identified by means of nuclear magnetic resonance spectroscopy (NMR) as well as high-resolution mass spectrometry (HR/MS). The identified compounds are caffeic acid (1), 3,4-dihydroxybenzoic acid (protocatechuic acid) (2), luteolin (3), diosmetin (4), 4-coumaroyl-4'-hydroxyl phenyllactic acid (5), rosmarinic acid (6), caffeoyl-4'-hydroxy-phenyllactic acid (isorinic acid) (7), apigenin 7-O-β-D-glucopyranoside (8), luteolin 7-O-β-D-glucopyranoside (9), and luteolin 7-sulfate (10). This is the first report to identify compounds 5 and 7 from the family Zosteraceae. The isolated compounds were assessed for their anti-aging abilities and were found to exhibit good anti-phototoxicity and anti-melanogenesis activities by increasing the viability of UVB-irradiated HaCaT cells by 6% to 34% and by inhibiting melanin synthesis in B16 melanoma cells by 44% to 65%.

Chloroplast genomic comparison provides insights into the evolution of seagrasses

BACKGROUND

Seagrasses are a polyphyletic group of monocotyledonous angiosperms that have evolved to live entirely submerged in marine waters. Thus, these species are ideal for studying plant adaptation to marine environments. Herein, we sequenced the chloroplast (cp) genomes of two seagrass species (Zostera muelleri and Halophila ovalis) and performed a comparative analysis of them with 10 previously published seagrasses, resulting in various novel findings.

RESULTS

The cp genomes of the seagrasses ranged in size from 143,877 bp (Zostera marina) to 178,261 bp (Thalassia hemprichii), and also varied in size among different families in the following order: Hydrocharitaceae > Cymodoceaceae > Ruppiaceae > Zosteraceae. The length differences between families were mainly related to the expansion and contraction of the IR region. In addition, we screened out 2,751 simple sequence repeats and 1,757 long repeat sequence types in the cp genome sequences of the 12 seagrass species, ultimately finding seven hot spots in coding regions. Interestingly, we found nine genes with positive selection sites, including two ATP subunit genes (atpA and atpF), three ribosome subunit genes (rps4, rps7, and rpl20), one photosystem subunit gene (psbH), and the ycf2, accD, and rbcL genes. These gene regions may have played critical roles in the adaptation of seagrasses to diverse environments. In addition, phylogenetic analysis strongly supported the division of the 12 seagrass species into four previously recognized major clades. Finally, the divergence time of the seagrasses inferred from the cp genome sequences was generally consistent with previous studies.

CONCLUSIONS

In this study, we compared chloroplast genomes from 12 seagrass species, covering the main phylogenetic clades. Our findings will provide valuable genetic data for research into the taxonomy, phylogeny, and species evolution of seagrasses.

The Structure of Genetic Diversity in Eelgrass (Zostera marina L.) along the North Pacific and Bering Sea Coasts of Alaska

Eelgrass (Zostera marina) populations occupying coastal waters of Alaska are separated by a peninsula and island archipelago into two Large Marine Ecosystems (LMEs). From populations in both LMEs, we characterize genetic diversity, population structure, and polarity in gene flow using nuclear microsatellite fragment and chloroplast and nuclear sequence data. An inverse relationship between genetic diversity and latitude was observed (heterozygosity: R2 = 0.738, P < 0.001; allelic richness: R2 = 0.327, P = 0.047), as was significant genetic partitioning across most sampling sites (θ = 0.302, P < 0.0001). Variance in allele frequency was significantly partitioned by region only in cases when a population geographically in the Gulf of Alaska LME (Kinzarof Lagoon) was instead included with populations in the Eastern Bering Sea LME (θp = 0.128-0.172; P < 0.003), suggesting gene flow between the two LMEs in this region. Gene flow among locales was rarely symmetrical, with notable exceptions generally following net coastal ocean current direction. Genetic data failed to support recent proposals that multiple Zostera species (i.e. Z. japonica and Z. angustifolia) are codistributed with Z. marina in Alaska. Comparative analyses also failed to support the hypothesis that eelgrass populations in the North Atlantic derived from eelgrass retained in northeastern Pacific Last Glacial Maximum refugia. These data suggest northeastern Pacific populations are derived from populations expanding northward from temperate populations following climate amelioration at the terminus of the last Pleistocene glaciation.

Seagrass radiation after Messinian salinity crisis reflected by strong genetic structuring and out-of-Africa scenario (Ruppiaceae)

Many aquatic plant and seagrass species are widespread and the origin of their continent-wide ranges might result from high gene flow levels. The response of species when extending northwards since the Last Glacial Maximum can be opposed to the structuring of their populations that survived glaciation cycles in southern regions. The peri-Mediterranean is a complex series of sea basins, coastlines, islands and river deltas with a unique history since the Messinian Crisis that potentially influenced allopatric processes of aquatic life. We tested whether vast ranges across Europe and the peri-Mediterranean of a global seagrass group (Ruppia species complexes) can be explained by either overall high levels of gene flow or vicariance through linking population genetics, phylogeography and shallow phylogenetics. A multigene approach identified haplogroup lineages of two species complexes, of ancient and recent hybrids with most of the diversity residing in the South. High levels of connectivity over long distances were only observed at recently colonized northern ranges and in recently-filled seas following the last glaciation. A strong substructure in the southern Mediterranean explained an isolation-by-distance model across Europe. The oldest lineages of the southern Mediterranean Ruppia dated back to the period between the end of the Messinian and Late Pliocene. An imprint of ancient allopatric origin was left at basin level, including basal African lineages. Thus both vicariance in the South and high levels of connectivity in the North explained vast species ranges. Our findings highlight the need for interpreting global distributions of these seagrass and euryhaline species in the context of their origin and evolutionary significant units for setting up appropriate conservation strategies.

Phylogenetic analyses of Zostera species based on rbcL and matK nucleotide sequences: Implications for the origin and diversification of seagrasses in Japanese waters

Seagrasses are composed of four families belonging to angiosperms and they are thought to become adaptive to aquatic life independently. Zosteraceae is one such family and because of the relatively high species diversity around Japan and Korea coast areas, the family might have arisen therefrom. To elucidate the origin and evolution of Zosteraceae which consists of three genera, Phyllospadix, Zostera, and Heterozostera, 2.8 kb nucleotide sequences of rbcL and matK genes in the chloroplast genome were examined for various species, including cosmopolitan Z. marina and endemic Z. caulescens. The phylogenetic analysis reveals the following three features. First, based on the synonymous nucleotide substitution rate of the rice chloroplast genome, we estimated the divergence times between Zosteraceae and its closest relative, Potamogetonaceae, and between different genera, Zostera and Phyllospadix, as approximately 100 million years (myr) and 36 myr, respectively, suggesting that Zosteraceae emerged somewhere in the period from 36 myr ago to 100 myr ago. Second, two subgenera of Zostera, Zostera and Zosterella, exhibit their reciprocal monophyly and appear to have differentiated from each other approximately 33 myr ago. However, the third genus Heterozostera branched off only 5 myr ago from the stem lineage leading to Zosterella and this seems too recent in comparison with the ancient divergence of the two subgenera. Third, we estimated the most recent common ancestor of subgenus Zostera as 6 myr. In Z. marina four haplotypes were found in the sample and have diversified in the past 1.5 myr. One haplotype is shared by both sides of the Japan Archipelago and its closely related haplotypes occur also in eastern Pacific Ocean. Based on these phylogeographic analyses, we propose a provisional age related classification of Zosteraceae to argue the origin and evolution.