Viroids and Viroid-like Circular RNAs: Do They Descend from Primordial Replicators?

Viroids are a unique class of plant pathogens that consist of small circular RNA molecules, between 220 and 450 nucleotides in size. Viroids encode no proteins and are the smallest known infectious agents. Viroids replicate via the rolling circle mechanism, producing multimeric intermediates which are cleaved to unit length either by ribozymes formed from both polarities of the viroid genomic RNA or by coopted host RNAses. Many viroid-like small circular RNAs are satellites of plant RNA viruses. Ribozyviruses, represented by human hepatitis delta virus, are larger viroid-like circular RNAs that additionally encode the viral nucleocapsid protein. It has been proposed that viroids are direct descendants of primordial RNA replicons that were present in the hypothetical RNA world. We argue, however, that much later origin of viroids, possibly, from recently discovered mobile genetic elements known as retrozymes, is a far more parsimonious evolutionary scenario. Nevertheless, viroids and viroid-like circular RNAs are minimal replicators that are likely to be close to the theoretical lower limit of replicator size and arguably comprise the paradigm for replicator emergence. Thus, although viroid-like replicators are unlikely to be direct descendants of primordial RNA replicators, the study of the diversity and evolution of these ultimate genetic parasites can yield insights into the earliest stages of the evolution of life.

Phylogenomics reveals the evolutionary origin of lichenization in chlorophyte algae

Mutualistic symbioses, such as lichens formed between fungi and green algae or cyanobacteria, have contributed to major transitions in the evolution of life and are at the center of extant ecosystems. However, our understanding of their evolution and function remains elusive in most cases. Here, we investigated the evolutionary history and the molecular innovations at the origin of lichens in green algae. We de novo sequenced the genomes or transcriptomes of 15 lichen-forming and closely-related non-lichen-forming algae and performed comparative phylogenomics with 22 genomes previously generated. We identified more than 350 functional categories significantly enriched in chlorophyte green algae able to form lichens. Among them, functions such as light perception or resistance to dehydration were shared between lichenizing and other terrestrial algae but lost in non-terrestrial ones, indicating that the ability to live in terrestrial habitats is a prerequisite for lichens to evolve. We detected lichen-specific expansions of glycosyl hydrolase gene families known to remodel cell walls, including the glycosyl hydrolase 8 which was acquired in lichenizing Trebouxiophyceae by horizontal gene transfer from bacteria, concomitantly with the ability to form lichens. Mining genome-wide orthogroups, we found additional evidence supporting at least two independent origins of lichen-forming ability in chlorophyte green algae. We conclude that the lichen-forming ability evolved multiple times in chlorophyte green algae, following a two-step mechanism which involves an ancestral adaptation to terrestrial lifestyle and molecular innovations to modify the partners cell walls.

BUILDING BLOCKS OF LIFE IN METEORITES MAY LEAD TO PANSPERMIA ORIGIN OF LIFE

The current hypothesis leads to the panspermia origin of life, which is based on the scientific principle of electromagnetic force interaction with matter. Electromagnetic force (Sunlight) interacts with inorganic chemistry available to us given out by the stars in the universe plausibly triggers the formation of extra-terrestrial biological molecules of proto cells under abiotic conditions, as evidenced by their presence in meteorites.' Proto cells’ might theoretically give rise to living organisms with a manifested soul, allowing 'Ribose' to be formed from ice grains hit by sunlight for RNA and DNA at the same time. The presence of life's building blocks and other important organic chemicals like ribose in meteorites, including some microscopic life forms that aren't native to Earth, may have led to the 'Panspermia Origin of Life' and the 'Evolution of Life on Earth' which is evidenced by the definition of 'Meteorites' in Vedic Scriptures, such as the "Bhagavad Gita" (3000 BC) and "Brihat Samhita" (520 AD) that they are the souls of righteous people who have returned to earth to be reborn.

The Owadów-Brzezinki geoeducation area at Sławno

The geoeducation area (called also “Owadów-Brzezinki Geopark”) located in the north-western margin of the Holy Cross Mountains (Tomaszów Syncline) at Sławno community (Łódź Voivodeship), was established in June 2019, in close vicinity of the Owadów-Brzezinki quarry. This locality is one of the most important palaeontological sites described recently in Poland. The area consists of the exhibition pavilion, educational routs and panoramic viewing platform, which is located along the edge of the quarry. The palaeontological exhibition shows the unique Late Jurassic fossils of marine and terrestrial organisms, many of them new to science, that have been excavated in the quarry during the last eight years. Among the most important fossils are: ammonites, lobster-like decapod crustaceans, horseshoe crabs, actinopterygian fish, a cryptodiran turtle, ichthyosaurs, as well as a small terrestrial crocodyliform, pterosaurs and insects. In addition to the original fossils, the exhibition presents life-size reconstructions of animals, that inhabited the local seas and islands during the Late Jurassic. The palaeontological sites of Owadów-Brzezinki is referred to as a new “taphonomic window” of the Late Jurassic, providing insights about the evolution of life on Earth in the palaeogeographical and palaeoenvironmental context.

The economics of organellar gene loss and endosymbiotic gene transfer

Background The endosymbiosis of the bacterial progenitors of the mitochondrion and the chloroplast are landmark events in the evolution of life on Earth. While both organelles have retained substantial proteomic and biochemical complexity, this complexity is not reflected in the content of their genomes. Instead, the organellar genomes encode fewer than 5% of the genes found in living relatives of their ancestors. While many of the 95% of missing organellar genes have been discarded, others have been transferred to the host nuclear genome through a process known as endosymbiotic gene transfer. Results Here, we demonstrate that the difference in the per-cell copy number of the organellar and nuclear genomes presents an energetic incentive to the cell to either delete organellar genes or transfer them to the nuclear genome. We show that, for the majority of transferred organellar genes, the energy saved by nuclear transfer exceeds the costs incurred from importing the encoded protein into the organelle where it can provide its function. Finally, we show that the net energy saved by endosymbiotic gene transfer can constitute an appreciable proportion of total cellular energy budgets and is therefore sufficient to impart a selectable advantage to the cell. Conclusion Thus, reduced cellular cost and improved energy efficiency likely played a role in the reductive evolution of mitochondrial and chloroplast genomes and the transfer of organellar genes to the nuclear genome.

Myelin sheath and cyanobacterial thylakoids as concentric multilamellar structures with similar bioenergetic properties

There is a surprisingly high morphological similarity between multilamellar concentric thylakoids in cyanobacteria and the myelin sheath that wraps the nerve axons. Thylakoids are multilamellar structures, which express photosystems I and II, cytochromes and ATP synthase necessary for the light-dependent reaction of photosynthesis. Myelin is a multilamellar structure that surrounds many axons in the nervous system and has long been believed to act simply as an insulator. However, it has been shown that myelin has a trophic role, conveying nutrients to the axons and producing ATP through oxidative phosphorylation. Therefore, it is tempting to presume that both membranous structures, although distant in the evolution tree, share not only a morphological but also a functional similarity, acting in feeding ATP synthesized by the ATP synthase to the centre of the multilamellar structure. Therefore, both molecular structures may represent a convergent evolution of life on Earth to fulfill fundamentally similar functions.

Catalytic Prebiotic Formation of Glycerol Phosphate Esters and an Estimation of Their Steady State Abundance under Plausible Early Earth Conditions

The emergence of biological phosphate esters of glycerol could have been a crucial step in the origin and evolution of life on the early Earth as glycerol phosphates today play a central role in biochemistry. We investigate here the formation of the glycerol phosphates by employing various rock samples, salts, and minerals as potential catalysts to aid the phosphorylation process. We report the synthesis of various phosphate esters of glycerol including glycerol-1-phosphate, glycerol-2-phosphate, cyclic glycerol-monophosphate as well as various diphosphate esters. Furthermore, the decomposition rates of glycerol phosphate under mild heating were also studied while keeping the pH constant. It was observed that glycerol phosphate starts decomposing quickly under mild heating conditions into inorganic orthophosphate and pyrophosphate, and a steady state concentration of ~0.5 M of glycerol phosphate may have been reasonable in ponds with abundant glycerol, phosphate, urea, and catalytic minerals.