Gain and loss of polyadenylation signals during evolution of green algae

<p>Abstract</p> <p>Background</p> <p>The Viridiplantae (green algae and land plants) consist of two monophyletic lineages: the Chlorophyta and the Streptophyta. Most green algae belong to the Chlorophyta, while the Streptophyta include all land plants and a small group of freshwater algae known as Charophyceae. Eukaryotes attach a poly-A tail to the 3' ends of most nuclear-encoded mRNAs. In embryophytes, animals and fungi, the signal for polyadenylation contains an A-rich sequence (often AAUAAA or related sequence) 13 to 30 nucleotides upstream from the cleavage site, which is commonly referred to as the near upstream element (NUE). However, it has been reported that the pentanucleotide UGUAA is used as polyadenylation signal for some genes in volvocalean algae.</p> <p>Results</p> <p>We set out to investigate polyadenylation signal differences between streptophytes and chlorophytes that may have emerged shortly after the evolutionary split between Streptophyta and Chlorophyta. We therefore analyzed expressed genes (ESTs) from three streptophyte algae, <it>Mesostigma viride</it>, <it>Klebsormidium subtile </it>and <it>Coleochaete scutata</it>, and from two early-branching chlorophytes, <it>Pyramimonas parkeae </it>and <it>Scherffelia dubia</it>. In addition, to extend the database, our analyses included ESTs from six other chlorophytes (<it>Acetabularia acetabulum</it>, <it>Chlamydomonas reinhardtii</it>, <it>Helicosporidium </it>sp. ex Simulium jonesii, <it>Prototheca wickerhamii, Scenedesmus obliquus </it>and <it>Ulva linza</it>) and one streptophyte (<it>Closterium peracerosum</it>). Our results indicate that polyadenylation signals in green algae vary widely. The UGUAA motif is confined to late-branching Chlorophyta. Most streptophyte algae do not have an A-rich sequence motif like that in embryophytes, animals and fungi. We observed polyadenylation signals similar to those of <it>Arabidopsis </it>and other land plants only in <it>Mesostigma</it>.</p> <p>Conclusion</p> <p>Polyadenylation signals in green algae show considerable variation. A new NUE (UGUAA) was invented in derived chlorophytes and replaced not only the A-rich NUE but the complete poly(A) signal in all chlorophytes investigated except <it>Scherffelia </it>(only NUE replaced) and <it>Pyramimonas </it>(UGUAA completely missing). The UGUAA element is completely absent from streptophytes. However, the structure of the poly(A) signal was often modified in streptophyte algae. In most species investigated, an A-rich NUE is missing; instead, these species seem to rely mainly on U-rich elements.</p

Origin of land plants: Do conjugating green algae hold the key?

<p>Abstract</p> <p>Background</p> <p>The terrestrial habitat was colonized by the ancestors of modern land plants about 500 to 470 million years ago. Today it is widely accepted that land plants (embryophytes) evolved from streptophyte algae, also referred to as charophycean algae. The streptophyte algae are a paraphyletic group of green algae, ranging from unicellular flagellates to morphologically complex forms such as the stoneworts (Charales). For a better understanding of the evolution of land plants, it is of prime importance to identify the streptophyte algae that are the sister-group to the embryophytes. The Charales, the Coleochaetales or more recently the Zygnematales have been considered to be the sister group of the embryophytes However, despite many years of phylogenetic studies, this question has not been resolved and remains controversial.</p> <p>Results</p> <p>Here, we use a large data set of nuclear-encoded genes (129 proteins) from 40 green plant taxa (Viridiplantae) including 21 embryophytes and six streptophyte algae, representing all major streptophyte algal lineages, to investigate the phylogenetic relationships of streptophyte algae and embryophytes. Our phylogenetic analyses indicate that either the Zygnematales or a clade consisting of the Zygnematales and the Coleochaetales are the sister group to embryophytes.</p> <p>Conclusions</p> <p>Our analyses support the notion that the Charales are not the closest living relatives of embryophytes. Instead, the Zygnematales or a clade consisting of Zygnematales and Coleochaetales are most likely the sister group of embryophytes. Although this result is in agreement with a previously published phylogenetic study of chloroplast genomes, additional data are needed to confirm this conclusion. A Zygnematales/embryophyte sister group relationship has important implications for early land plant evolution. If substantiated, it should allow us to address important questions regarding the primary adaptations of viridiplants during the conquest of land. Clearly, the biology of the Zygnematales will receive renewed interest in the future.</p

Gain and loss of polyadenylation signals during evolution of green algae-1

<p><b>Copyright information:</b></p><p>Taken from "Gain and loss of polyadenylation signals during evolution of green algae"</p><p>http://www.biomedcentral.com/1471-2148/7/65</p><p>BMC Evolutionary Biology 2007;7():65-65.</p><p>Published online 18 Apr 2007</p><p>PMCID:PMC1868727.</p><p></p>U-rich within 50 nt upstream from the CS in different chlorophyte and streptophyte algae

Gain and loss of polyadenylation signals during evolution of green algae-2

<p><b>Copyright information:</b></p><p>Taken from "Gain and loss of polyadenylation signals during evolution of green algae"</p><p>http://www.biomedcentral.com/1471-2148/7/65</p><p>BMC Evolutionary Biology 2007;7():65-65.</p><p>Published online 18 Apr 2007</p><p>PMCID:PMC1868727.</p><p></p> is indicated. Loss of the AAUAAA-like signal is indicated with a red arrow and the gain of the UGUAA signal is indicated with a purple arrow

Geographic distance and mountain ranges structure freshwater protist communities on a European scalе

Protists influence ecosystems by modulating microbial population size, diversity, metabolic outputs and gene flow. In this study we used eukaryotic ribosomal amplicon diversity from 218 European freshwater lakes sampled in August 2012 to assess the effect of mountain ranges as biogeographic barriers on spatial patterns and microbial community structure in European freshwaters. The diversity of microbial communities as reflected by amplicon clusters suggested that the eukaryotic microbial inventory of lakes was well-sampled at the European and at the local scale. Our pan-European diversity analysis indicated that biodiversity and richness of high mountain lakes differed from that of lowland lakes. Further, the taxon inventory of high-mountain lakes strongly contributed to beta-diversity despite a low taxon inventory. Even though ecological factors, in general, strongly affect protist community pattern, we show that geographic distance and geographic barriers significantly contribute to community composition particularly for high mountain regions which presumably act as biogeographic islands. However, community composition in lowland lakes was also affected by geographic distance but less pronounced as in high mountain regions. In consequence protist populations are locally structured into distinct biogeographic provinces and community analyses revealed biogeographic patterns also for lowland lakes whereby European mountain ranges act as dispersal barriers in particular for short to intermediate distances whereas the effect of mountain ranges levels off on larger scale