Dicranochaete - an enigmatic green alga with surprising adaptive capabilities

Dicranochaete is a green coccoid alga with a spiny cap and a long branched seta that was described more than 100 yr ago from field samples. Although Dicranochaete has been repeatedly reported to be found on Sphagnum 'leaves' in peat bogs, our knowledge about its development is still fragmentary, and its phylogenetic affiliation remained controversial. To advance knowledge about this lesser-known alga, I used two Dicranochaete strains, grew them in a medium that mimics chemical properties of peat bogs and studied their life history and development. Furthermore, phylogenetic analyses using rDNA sequence comparisons were performed. My studies resulted in the following key observations: (1) Dicranochaete possesses a unique development that together with its characteristic morphology likely represents adaptations to the specific environment of peat bogs: the spiny cap, especially in early stages of algal development, presumably serves as a defence against predators. The seta provides an additional surface area to aid the uptake of nutrients, in particular phosphate. (2) Phylogenetic analyses identified Dicranochaete as a member of the Chaetopeltidales (Chlorophyceae). Moreover, a new species of Dicranochaete, Dicranochaete variabilis sp. nov., was erected, and the genus Dicranochaete Hieronymus (1890) was emended. In conclusion, this study provides new insights into the life history, developmental processes and phylogenetic position of Dicranochaete and provides insights into adaptation of epiphyllous microalgae to nutrient-poor environments (i.e. peat bogs)

Draparnaldia: a chlorophyte model for comparative analyses of plant terrestrialization

It is generally accepted that land plants evolved from streptophyte algae. However, there are also many chlorophytes (a sister group of streptophyte algae and land plants) that moved to terrestrial habitats and even resemble mosses. This raises the question of why no land plants evolved from chlorophytes. In order to better understand what enabled streptophyte algae to conquer the land, it is necessary to study the chlorophytes as well. This review will introduce the freshwater filamentous chlorophyte alga Draparnaldia sp. (Chaetophorales, Chlorophyceae) as a model for comparative analyses between these two lineages. It will also focus on current knowledge about the evolution of morphological complexity in chlorophytes versus streptophytes and their respective morphological/behavioural adaptations to semi-terrestrial habitats, and will show why Draparnaldia is needed as a new model system

The Chaetophorales (Chlorophyceae) - a taxonomic revision at family level

The Chaetophorales (Chlorophyceae) consist of filamentous green algae that were mostly described directly from natural samples by light microscopy. However, the descriptions were often based on morphological characters that are either homoplasious or sensitive to environmental factors. This clearly prevents proper identification of several chaetophoralean taxa and highlights the need for taxonomic revision at different taxonomic levels. In the present study, we focused on revision of the Chaetophorales at the family level. We used a well-resolved molecular phylogeny to re-evaluate morphological characters in the Chaetophorales under clearly defined laboratory conditions. We identified five morphological characters that permitted unambiguous identification of most chaetophoralean families, and used these characters to establish a new family, the Fritschiellaceae (fam. nov.), and emend the Chaetophoraceae Greville 1824. Knowledge gained from this study lends additional weight to the current classification of the Chaetophorales and may serve as an example for taxonomic revisions of other complex filamentous algae

Evolution of Helix Formation in the Ribosomal Internal Transcribed Spacer 2 (ITS2) and Its Significance for RNA Secondary Structures

Helices are the most common elements of RNA secondary structure. Despite intensive investigations of various types of RNAs, the evolutionary history of the formation of new helices (novel helical structures) remains largely elusive. Here, by studying the nuclear ribosomal Internal Transcribed Spacer 2 (ITS2), a fast-evolving part of the eukaryotic nuclear ribosomal operon, we identify two possible types of helix formation: one type is dichotomous helix formationaEurotransition from one large helix to two smaller helices by invagination of the apical part of a helix, which significantly changes the shape of the original secondary structure but does not increase its complexity (i.e., the total length of the RNA). An alternative type is lateral helix formationaEuroorigin of an extra helical region by the extension of a bulge loop or a spacer in a multi-helix loop of the original helix, which does not disrupt the pre-existing structure but increases RNA size. Moreover, we present examples from the RNA sequence literature indicating that both types of helix formation may have implications for RNA evolution beyond ITS2

Regeneration and transient gene expression in protoplasts of Draparnaldia (chlorophytes), an emerging model for comparative analyses with basal streptophytes

BackgroundGreen plants comprise two lineages: (1) the streptophytes that colonised land and (2) the chlorophytes that have adaptations to land but remained mostly aquatic. To better understand what made streptophytes so successful, we are currently establishing the chlorophyte alga Draparnaldia sp. (Chaetophorales, Chlorophyceae) as a model for comparative analyses between these two lineages. However, establishing Draparnaldia as a valuable model requires that it can be transformed. Thus, our goal is to develop a transformation protocol for this alga.ResultsWe have established the first transformation protocol for Draparnaldia. This protocol is based on protoplast transformation by electroporation. It includes instructions on protoplast isolation, regeneration and transient transfection. It also provides a list of the effective selective agents for future Draparnaldia transformations.ConclusionsOur protocol opens a way for Draparnaldia functional genomics analyses. Moreover, it also provides an important base for establishment of stable transformation

Barrancaceae: A new green algal lineage with structural and behavioral adaptations to a fluctuating environment

PREMISE OF THE STUDY: To enhance our knowledge of the diversity of microalgae, a phycological survey of the Canary Islands (Spain) was undertaken. Here we report the discovery of a (semi)terrestrial green filamentous alga isolated from a steep volcanic canyon on La Palma. This alga is continually exposed to changing weather conditions (floods vs.droughts) and thus provides a good opportunity to investigate possible adaptations to a semiterrestrial habitat with large fluctuations of environmental parameters. METHODS: We used axenic cultures, simulated flood and drought stresses and studied their effect on the life history of the alga using light, confocal laser scanning and scanning electron microscopy including fluorescent staining. Furthermore, phylogenetic analyses using rDNA sequence comparisons were performed. KEY RESULTS: Three specific life-history traits that likely represent adaptations to the fluctuating environment of the canyon were observed: (1) fragmentation through filament splitting, a unique branching mechanism not reported before in algae and initiated by formation of oblique cross walls, (2) apla-nospore formation, and (3) reproduction by multiflagellate zoospores with 4-24 flagella arranged in groups of four. Phylogenetic analyses identified the alga as Barranca multiflagellata gen.et sp.nov. (Barrancaceae fam.nov., Chaetophorales, Chlorophyceae). Moreover, the Chaetophoraceae Greville, 1824 was emended and a new family, Uronemataceae (fam.nov.) erected. CONCLUSIONS: The discovery of Barrancaceae fam.nov. highlights the importance of investigating nonconventional habitats to explore microalgal diversity. The reproductive versatility demonstrated by Barranca suggests adaptation to a semiterrestrial habitat with large fluctuations in water availability

A Survey of Empirical Results on Program Slicing

International audienceBACKGROUND:Patients with peripheral artery disease have an increased risk of cardiovascular morbidity and mortality. Antiplatelet agents are widely used to reduce these complications.METHODS:This was a multicentre, double-blind, randomised placebo-controlled trial for which patients were recruited at 602 hospitals, clinics, or community practices from 33 countries across six continents. Eligible patients had a history of peripheral artery disease of the lower extremities (previous peripheral bypass surgery or angioplasty, limb or foot amputation, intermittent claudication with objective evidence of peripheral artery disease), of the carotid arteries (previous carotid artery revascularisation or asymptomatic carotid artery stenosis of at least 50%), or coronary artery disease with an ankle-brachial index of less than 0·90. After a 30-day run-in period, patients were randomly assigned (1:1:1) to receive oral rivaroxaban (2·5 mg twice a day) plus aspirin (100 mg once a day), rivaroxaban twice a day (5 mg with aspirin placebo once a day), or to aspirin once a day (100 mg and rivaroxaban placebo twice a day). Randomisation was computer generated. Each treatment group was double dummy, and the patient, investigators, and central study staff were masked to treatment allocation. The primary outcome was cardiovascular death, myocardial infarction or stroke; the primary peripheral artery disease outcome was major adverse limb events including major amputation. This trial is registered with ClinicalTrials.gov, number NCT01776424, and is closed to new participants.FINDINGS:Between March 12, 2013, and May 10, 2016, we enrolled 7470 patients with peripheral artery disease from 558 centres. The combination of rivaroxaban plus aspirin compared with aspirin alone reduced the composite endpoint of cardiovascular death, myocardial infarction, or stroke (126 [5%] of 2492 vs 174 [7%] of 2504; hazard ratio [HR] 0·72, 95% CI 0·57-0·90, p=0·0047), and major adverse limb events including major amputation (32 [1%] vs 60 [2%]; HR 0·54 95% CI 0·35-0·82, p=0·0037). Rivaroxaban 5 mg twice a day compared with aspirin alone did not significantly reduce the composite endpoint (149 [6%] of 2474 vs 174 [7%] of 2504; HR 0·86, 95% CI 0·69-1·08, p=0·19), but reduced major adverse limb events including major amputation (40 [2%] vs 60 [2%]; HR 0·67, 95% CI 0·45-1·00, p=0·05). The median duration of treatment was 21 months. The use of the rivaroxaban plus aspirin combination increased major bleeding compared with the aspirin alone group (77 [3%] of 2492 vs 48 [2%] of 2504; HR 1·61, 95% CI 1·12-2·31, p=0·0089), which was mainly gastrointestinal. Similarly, major bleeding occurred in 79 (3%) of 2474 patients with rivaroxaban 5 mg, and in 48 (2%) of 2504 in the aspirin alone group (HR 1·68, 95% CI 1·17-2·40; p=0·0043).INTERPRETATION:Low-dose rivaroxaban taken twice a day plus aspirin once a day reduced major adverse cardiovascular and limb events when compared with aspirin alone. Although major bleeding was increased, fatal or critical organ bleeding was not. This combination therapy represents an important advance in the management of patients with peripheral artery disease. Rivaroxaban alone did not significantly reduce major adverse cardiovascular events compared with asprin alone, but reduced major adverse limb events and increased major bleeding