The RNA world concept1 is one of the most fundamental pillars of the origin of life theory2–4. It predicts that life evolved from increasingly complex self-replicating RNA molecules1,2,4. The question of how this RNA world then advanced to the next stage, in which proteins became the catalysts of life and RNA reduced its function predominantly to information storage, is one of the most mysterious chicken-and-egg conundrums in evolution3–5. Here we show that non-canonical RNA bases, which are found today in transfer and ribosomal RNAs6,7, and which are considered to be relics of the RNA world8–12, are able to establish peptide synthesis directly on RNA. The discovered chemistry creates complex peptide-decorated RNA chimeric molecules, which suggests the early existence of an RNA–peptide world13 from which ribosomal peptide synthesis14 may have emerged15,16. The ability to grow peptides on RNA with the help of non-canonical vestige nucleosides offers the possibility of an early co-evolution of covalently connected RNAs and peptides13,17,18, which then could have dissociated at a higher level of sophistication to create the dualistic nucleic acid–protein world that is the hallmark of all life on Earth.

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SummaryArchaea may be involved in global energy cycles, and are known for their ability to interact with eukaryotic species (sponges, corals and ascidians) or as archaeal-bacterial consortia. The recently proposed phylum Thaumarchaeota may represent the deepest branching lineage in the archaeal phylogeny emerging before the divergence between Euryarchaeota and Crenarchaeota. Here we report the first characterization of two marine thaumarchaeal species from shallow waters that consist of multiple giant cells. One species is coated with sulfur-oxidizing g-Proteobacteria. These new uncultured thaumarchaeal species are able to live in the sulfide-rich environments of a tropical mangrove swamp, either on living tissues such as roots or on various kinds of materials such as stones, sunken woods, etc. These archaea and archaea/bacteria associations have been studied using light microscopy, transmission electron microscopy and scanning electron microscopy. Species identification of archaeons and the putative bacterial symbiont have been assessed by 16S small subunit ribosomal RNA analysis. The sulfur-oxidizing ability of the bacteria has been assessed by genetic investigation on alpha-subunit of the adenosine-5Ј-phosphosulfate reductase/oxidase's (AprA). Species identifications have been confirmed by fluorescence in situ hybridization using specific probes designed in this study. In this article, we describe two new giant archaeal species that form the biggest archaeal filaments ever observed. One of these species is covered by a specific biofilm of sulfur-oxidizing g-Proteobacteria. This study highlights an unexpected morphological and genetic diversity of the phylum Thaumarchaeota.

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We analysed the molecular diversity of Pterocarpus officinalis, a tree species distributed in Caribbean islands, South and Central America to quantify the genetic variation within island, to assess the pattern of differentiation and infer levels of gene flow; with the overall goal of defining a strategy of conservation. Two hundred two individuals of 9 populations were analysed using three chloroplast and six nuclear microsatellite markers. The observed heterozygosity varied markedly among the populations for nuclear (H(Onuc )= 0.20-0.50) and chloroplast microsatellites (H (cp )= 0.22-0.68). The continental population from French Guyana showed a higher value of H(Onuc) than island populations, and the differences were significant in some cases. The fixation index F (IS) ranged from -0.043 to 0.368; a significant heterozygote deficit was detected in 7 populations. The heterozygosity excess method suggested that two populations in Guadeloupe have undergone a recent bottleneck. Global and pairwise F (ST) were high for both nuclear (F(STnuc )= 0.29) and chloroplast microsatellites (F(STcp )= 0.58). The neighbour-joining tree based on both markers, presented a differentiation pattern that can be explained by the seed dispersal by flotation and marine stream. The comparison of Bayesian approach and the method based on allelic frequency demonstrate a very limited number of migrants between populations.

The purpose of this study was to test the capacity of the ectomycorrhizal (ECM) fungus, Scleroderma bermudense, to alleviate saline stress in seagrape (Coccoloba uvifera L.) seedlings. Plants were grown over a range (0, 200, 350 and 500 mM) of NaCl levels for 12 weeks, after 4 weeks of non-saline pre-treatment under greenhouse conditions. Growth and mineral nutrition of the seagrape seedlings were stimulated by S. bermudense regardless of salt stress. Although ECM colonization was reduced with increasing NaCl levels, ECM dependency of seagrape seedlings increased. Tissues of ECM plants had significantly increased concentrations of P and K but lower Na and Cl concentrations than those of non-ECM plants. Higher K concentrations in the leaves of ECM plants suggested a higher osmoregulating capacity of these plants. Moreover, the water status of ECM plants was improved despite their higher evaporative leaf surface. The results suggest that the reduction in Na and Cl uptake together with a concomitant increase in P and K absorption and a higher water status in ECM plants may be important salt-alleviating mechanisms for seagrape seedlings growing in saline soils.

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