A complete ancient RNA genome: identification, reconstruction and evolutionary history of archaeological Barley Stripe Mosaic Virus

Distribution of Wheat-Infecting Viruses and Genetic Variability of Wheat Streak Mosaic Virus and Barley Stripe Mosaic Virus in Kazakhstan

Wheat is an essential cereal crop for the economy and food safety of Kazakhstan. In the present work, a screening of wheat and barley from different regions of Kazakhstan was conducted using newly developed specific primers for reverse transcription PCR and loop-mediated isothermal amplification (LAMP) assays. In total, 82 and 19 of 256 samples of wheat and barley tested positive for wheat streak mosaic virus (WSMV) and barley stripe mosaic virus (BSMV), respectively. A phylogenetic analysis using two independent methods revealed that most of the analyzed isolates had a European origin. Molecular data on the distribution and diversity of cereal viruses in Kazakhstan were obtained for the first time and will help lay a foundation for the implementation of genetics and genomics in wheat phyto-epidemiology in the country.

Paleomicrobiology: Tracking the past microbial life from single species to entire microbial communities

By deciphering information encoded in degraded ancient DNA extracted from up to million-years-old samples, molecular paleomicrobiology enables to objectively retrace the temporal evolution of microbial species and communities. Assembly of full-length genomes of ancient pathogen lineages allows not only to follow historical epidemics in space and time but also to identify the acquisition of genetic features that represent landmarks in the evolution of the host-microbe interaction. Analysis of microbial community DNA extracted from essentially human paleo-artefacts (paleofeces, dental calculi) evaluates the relative contribution of diet, lifestyle and geography on the taxonomic and functional diversity of these guilds in which have been identified species that may have gone extinct in today's human microbiome. As for non-host-associated environmental samples, such as stratified sediment cores, analysis of their DNA illustrates how and at which pace microbial communities are affected by local or widespread environmental disturbance. Description of pre-disturbance microbial diversity patterns can aid in evaluating the relevance and effectiveness of remediation policies. We finally discuss how recent achievements in paleomicrobiology could contribute to microbial biotechnology in the fields of medical microbiology and food science to trace the domestication of microorganisms used in food processing or to illustrate the historic evolution of food processing microbial consortia.

Revisiting the origins of the Sobemovirus genus: A case for ancient origins of plant viruses

The discrepancy between short- and long-term rate estimates, known as the time-dependent rate phenomenon (TDRP), poses a challenge to extrapolating evolutionary rates over time and reconstructing evolutionary history of viruses. The TDRP reveals a decline in evolutionary rate estimates with the measurement timescale, explained empirically by a power-law rate decay, notably observed in animal and human viruses. A mechanistic evolutionary model, the Prisoner of War (PoW) model, has been proposed to address TDRP in viruses. Although TDRP has been studied in animal viruses, its impact on plant virus evolutionary history remains largely unexplored. Here, we investigated the consequences of TDRP in plant viruses by applying the PoW model to reconstruct the evolutionary history of sobemoviruses, plant pathogens with significant importance due to their impact on agriculture and plant health. Our analysis showed that the Sobemovirus genus dates back over four million years, indicating an ancient origin. We found evidence that supports deep host jumps to Poaceae, Fabaceae, and Solanaceae occurring between tens to hundreds of thousand years ago, followed by specialization. Remarkably, the TDRP-corrected evolutionary history of sobemoviruses was extended far beyond previous estimates that had suggested their emergence nearly 9,000 years ago, a time coinciding with the Neolithic period in the Near East. By incorporating sequences collected through metagenomic analyses, the resulting phylogenetic tree showcases increased genetic diversity, reflecting a deep history of sobemovirus species. We identified major radiation events beginning between 4,600 to 2,000 years ago, which aligns with the Neolithic period in various regions, suggesting a period of rapid diversification from then to the present. Our findings make a case for the possibility of deep evolutionary origins of plant viruses.

A Glimpse into the Past: What Ancient Viral Genomes Reveal About Human History

Humans have battled viruses for millennia. However, directly linking the symptomatology of disease outbreaks to specific viral pathogens was not possible until the twentieth century. With the advent of the genomic era and the development of advanced protocols for isolation, sequencing, and analysis of ancient nucleic acids from diverse human remains, the identification and characterization of ancient viruses became feasible. Recent studies have provided invaluable information about past epidemics and made it possible to examine assumptions and inferences on the origin and evolution of certain viral families. In parallel, the study of ancient viruses also uncovered their importance in the evolution of the human lineage and their key roles in shaping major events in human history. In this review, we describe the strategies used for the study of ancient viruses, along with their limitations, and provide a detailed account of what past viral infections have revealed about human history.

Historical RNA expression profiles from the extinct Tasmanian tiger

Paleogenomics continues to yield valuable insights into the evolution, population dynamics, and ecology of our ancestors and other extinct species. However, DNA sequencing cannot reveal tissue-specific gene expression, cellular identity, or gene regulation, which are only attainable at the transcriptional level. Pioneering studies have shown that useful RNA can be extracted from ancient specimens preserved in permafrost and historical skins from extant canids, but no attempts have been made so far on extinct species. We extract, sequence, and analyze historical RNA from muscle and skin tissue of a ∼130-year-old Tasmanian tiger (Thylacinus cynocephalus) preserved in desiccation at room temperature in a museum collection. The transcriptional profiles closely resemble those of extant species, revealing specific anatomical features such as slow muscle fibers or blood infiltration. Metatranscriptomic analysis, RNA damage, tissue-specific RNA profiles, and expression hotspots genome-wide further confirm the thylacine origin of the sequences. RNA sequences are used to improve protein-coding and noncoding annotations, evidencing missing exonic loci and the location of ribosomal RNA genes while increasing the number of annotated thylacine microRNAs from 62 to 325. We discover a thylacine-specific microRNA isoform that could not have been confirmed without RNA evidence. Finally, we detect traces of RNA viruses, suggesting the possibility of profiling viral evolution. Our results represent the first successful attempt to obtain transcriptional profiles from an extinct animal species, providing thought-to-be-lost information on gene expression dynamics. These findings hold promising implications for the study of RNA molecules across the vast collections of natural history museums and from well-preserved permafrost remains.

Herbarium specimen sequencing allows precise dating of Xanthomonas citri pv. citri diversification history

Herbarium collections are an important source of dated, identified and preserved DNA, whose use in comparative genomics and phylogeography can shed light on the emergence and evolutionary history of plant pathogens. Here, we reconstruct 13 historical genomes of the bacterial crop pathogen Xanthomonas citri pv. citri (Xci) from infected Citrus herbarium specimens. Following authentication based on ancient DNA damage patterns, we compare them with a large set of modern genomes to estimate their phylogenetic relationships, pathogenicity-associated gene content and several evolutionary parameters. Our results indicate that Xci originated in Southern Asia ~11,500 years ago (perhaps in relation to Neolithic climate change and the development of agriculture) and diversified during the beginning of the 13th century, after Citrus diversification and before spreading to the rest of the world (probably via human-driven expansion of citriculture through early East-West trade and colonization).

The Role of Ancient Grains in Alleviating Hunger and Malnutrition

Meeting the United Nation's sustainable development goals for zero hunger becomes increasingly challenging with respect to climate change and political and economic challenges. An effective strategy to alleviate hunger and its severe implications is to produce affordable, nutrient-dense, and sustainable food products. Ancient grains were long-forgotten due to the dominance of modern grains, but recently, they have been rediscovered as highly nutritious, healthy and resilient grains for solving the nutrition demand and food supply chain problems. This review article aims to critically examine the progress in this emerging field and discusses the potential roles of ancient grains in the fight against hunger. We provide a comparative analysis of different ancient grains with their modern varieties in terms of their physicochemical properties, nutritional profiles, health benefits and sustainability. A future perspective is then introduced to highlight the existing challenges of using ancient grains to help eradicate world hunger. This review is expected to guide decision-makers across different disciplines, such as food, nutrition and agronomy, and policymakers in taking sustainable actions against malnutrition and hunger.

Advances in experimental and computational methodologies for the study of microbial-surface interactions at different omics levels

The study of the biological response of microbial cells interacting with natural and synthetic interfaces has acquired a new dimension with the development and constant progress of advanced omics technologies. New methods allow the isolation and analysis of nucleic acids, proteins and metabolites from complex samples, of interest in diverse research areas, such as materials sciences, biomedical sciences, forensic sciences, biotechnology and archeology, among others. The study of the bacterial recognition and response to surface contact or the diagnosis and evolution of ancient pathogens contained in archeological tissues require, in many cases, the availability of specialized methods and tools. The current review describes advances in in vitro and in silico approaches to tackle existing challenges (e.g., low-quality sample, low amount, presence of inhibitors, chelators, etc.) in the isolation of high-quality samples and in the analysis of microbial cells at genomic, transcriptomic, proteomic and metabolomic levels, when present in complex interfaces. From the experimental point of view, tailored manual and automatized methodologies, commercial and in-house developed protocols, are described. The computational level focuses on the discussion of novel tools and approaches designed to solve associated issues, such as sample contamination, low quality reads, low coverage, etc. Finally, approaches to obtain a systems level understanding of these complex interactions by integrating multi omics datasets are presented.

A Timeframe for SARS-CoV-2 Genomes: A Proof of Concept for Postmortem Interval Estimations

Establishing the timeframe when a particular virus was circulating in a population could be useful in several areas of biomedical research, including microbiology and legal medicine. Using simulations, we demonstrate that the circulation timeframe of an unknown SARS-CoV-2 genome in a population (hereafter, estimated time of a queried genome [QG]; tE-QG) can be easily predicted using a phylogenetic model based on a robust reference genome database of the virus, and information on their sampling dates. We evaluate several phylogeny-based approaches, including modeling evolutionary (substitution) rates of the SARS-CoV-2 genome (~10-3 substitutions/nucleotide/year) and the mutational (substitutions) differences separating the QGs from the reference genomes (RGs) in the database. Owing to the mutational characteristics of the virus, the present Viral Molecular Clock Dating (VMCD) method covers timeframes going backwards from about a month in the past. The method has very low errors associated to the tE-QG estimates and narrow intervals of tE-QG, both ranging from a few days to a few weeks regardless of the mathematical model used. The SARS-CoV-2 model represents a proof of concept that can be extrapolated to any other microorganism, provided that a robust genome sequence database is available. Besides obvious applications in epidemiology and microbiology investigations, there are several contexts in forensic casework where estimating tE-QG could be useful, including estimation of the postmortem intervals (PMI) and the dating of samples stored in hospital settings.

Historic and Prehistoric Epidemics: An Overview of Sources Available for the Study of Ancient Pathogens

Since life on earth developed, parasitic microbes have thrived. Increases in host numbers, or the conquest of a new species, provide an opportunity for such a pathogen to enjoy, before host defense systems kick in, a similar upsurge in reproduction. Outbreaks, caused by "endemic" pathogens, and epidemics, caused by "novel" pathogens, have thus been creating chaos and destruction since prehistorical times. To study such (pre)historic epidemics, recent advances in the ancient DNA field, applied to both archeological and historical remains, have helped tremendously to elucidate the evolutionary trajectory of pathogens. These studies have offered new and unexpected insights into the evolution of, for instance, smallpox virus, hepatitis B virus, and the plague-causing bacterium Yersinia pestis. Furthermore, burial patterns and historical publications can help in tracking down ancient pathogens. Another source of information is our genome, where selective sweeps in immune-related genes relate to past pathogen attacks, while multiple viruses have left their genomes behind for us to study. This review will discuss the sources available to investigate (pre)historic diseases, as molecular knowledge of historic and prehistoric pathogens may help us understand the past and the present, and prepare us for future epidemics.

Exploring the Emergence and Evolution of Plant Pathogenic Microbes Using Historical and Paleontological Sources

Biotechnological advances now permit broad exploration of past microbial communities preserved in diverse substrates. Despite biomolecular degradation, high-throughput sequencing of preserved materials can yield invaluable genomic and metagenomic data from the past. This line of research has expanded from its initial human- and animal-centric foci to include plant-associated microbes (viruses, archaea, bacteria, fungi, and oomycetes), for which historical, archaeological, and paleontological data illuminate past epidemics and evolutionary history. Genetic mechanisms underlying the acquisition of microbial pathogenicity, including hybridization, polyploidization, and horizontal gene transfer, can now be reconstructed, as can gene-for-gene coevolution with plant hosts. Epidemiological parameters, such as geographic origin and range expansion, can also be assessed. Building on published case studies with individual phytomicrobial taxa, the stage is now set for broader, community-wide studies of preserved plant microbiomes to strengthen mechanistic understanding of microbial interactions and plant disease emergence.

A comparative study of RNA yields from museum specimens, including an optimized protocol for extracting RNA from formalin-fixed specimens

Animal specimens in natural history collections are invaluable resources in examining the historical context of pathogen dynamics in wildlife and spillovers to humans. For example, natural history specimens may reveal new associations between bat species and coronaviruses. However, RNA viruses are difficult to study in historical specimens because protocols for extracting RNA from these specimens have not been optimized. Advances have been made in our ability to recover nucleic acids from formalin-fixed paraffin-embedded samples (FFPE) commonly used in human clinical studies, yet other types of formalin preserved samples have received less attention. Here, we optimize the recovery of RNA from formalin-fixed ethanol-preserved museum specimens in order to improve the usability of these specimens in surveys for zoonotic diseases. We provide RNA quality and quantity measures for replicate tissues subsamples of 22 bat specimens from five bat genera (Rhinolophus, Hipposideros, Megareops, Cynopterus, and Nyctalus) collected in China and Myanmar from 1886 to 2003. As tissues from a single bat specimen were preserved in a variety of ways, including formalin-fixed (8 bats), ethanol-preserved and frozen (13 bats), and flash frozen (2 bats), we were able to compare RNA quality and yield across different preservation methods. RNA extracted from historical museum specimens is highly fragmented, but usable for short-read sequencing and targeted amplification. Incubation of formalin-fixed samples with Proteinase-K following thorough homogenization improves RNA yield. This optimized protocol extends the types of data that can be derived from existing museum specimens and facilitates future examinations of host and pathogen RNA from specimens.

A New Method for Rapid Subcellular Localization and Gene Function Analysis in Cotton Based on Barley Stripe Mosaic Virus

The difficulty of genetic transformation has restricted research on functional genomics in cotton. Thus, a rapid and efficient method for gene overexpression that does not rely on genetic transformation is needed. Virus-based vectors offer a reasonable alternative for protein expression, as viruses can infect the host systemically to achieve expression and replication without transgene integration. Previously, a novel four-component barley stripe mosaic virus (BSMV) was reported to overexpress large fragments of target genes in plants over a long period of time, which greatly simplified the study of gene overexpression. However, whether this system can infect cotton and stably overexpress target genes has not yet been studied. In this study, we verified that this new BSMV system can infect cotton through seed imbibition and systemically overexpress large fragments of genes (up to 2340 bp) in cotton. The target gene that was fused with GFP was expressed at a high level in the roots, stems, and cotyledons of cotton seedlings, and stable fluorescence signals were detected in the cotton roots and leaves even after 4 weeks. Based on the BSMV overexpression system, the subcellular localization marker line of endogenous proteins localized in the nucleus, endoplasmic reticulum, plasma membrane, Golgi body, mitochondria, peroxisomes, tonoplast, and plastids were quickly established. The overexpression of a cotton Bile Acid Sodium Symporter GhBASS5 using the BSMV system indicated that GhBASS5 negatively regulated salt tolerance in cotton by transporting Na⁺ from underground to the shoots. Furthermore, multiple proteins were co-delivered, enabling co-localization and the study of protein–protein interactions through co-transformation. We also confirmed that the BSMV system can be used to conduct DNA-free gene editing in cotton by delivering split-SpCas9/sgRNA. Ultimately, the present work demonstrated that this BSMV system could be used as an efficient overexpression system for future cotton gene function research.

Detection of Ancient Viruses and Long-Term Viral Evolution

The COVID-19 outbreak has reminded us of the importance of viral evolutionary studies as regards comprehending complex viral evolution and preventing future pandemics. A unique approach to understanding viral evolution is the use of ancient viral genomes. Ancient viruses are detectable in various archaeological remains, including ancient people's skeletons and mummified tissues. Those specimens have preserved ancient viral DNA and RNA, which have been vigorously analyzed in the last few decades thanks to the development of sequencing technologies. Reconstructed ancient pathogenic viral genomes have been utilized to estimate the past pandemics of pathogenic viruses within the ancient human population and long-term evolutionary events. Recent studies revealed the existence of non-pathogenic viral genomes in ancient people's bodies. These ancient non-pathogenic viruses might be informative for inferring their relationships with ancient people's diets and lifestyles. Here, we reviewed the past and ongoing studies on ancient pathogenic and non-pathogenic viruses and the usage of ancient viral genomes to understand their long-term viral evolution.

Contribution of historical herbarium small RNAs to the reconstruction of a cassava mosaic geminivirus evolutionary history

Emerging viral diseases of plants are recognised as a growing threat to global food security. However, little is known about the evolutionary processes and ecological factors underlying the emergence and success of viruses that have caused past epidemics. With technological advances in the field of ancient genomics, it is now possible to sequence historical genomes to provide a better understanding of viral plant disease emergence and pathogen evolutionary history. In this context, herbarium specimens represent a valuable source of dated and preserved material. We report here the first historical genome of a crop pathogen DNA virus, a 90-year-old African cassava mosaic virus (ACMV), reconstructed from small RNA sequences bearing hallmarks of small interfering RNAs. Relative to tip-calibrated dating inferences using only modern data, those performed with the historical genome yielded both molecular evolution rate estimates that were significantly lower, and lineage divergence times that were significantly older. Crucially, divergence times estimated without the historical genome appeared in discordance with both historical disease reports and the existence of the historical genome itself. In conclusion, our study reports an updated time-frame for the history and evolution of ACMV and illustrates how the study of crop viral diseases could benefit from natural history collections.

Identification and Molecular Characterization of a Novel Hordeivirus Associated With Yellow Mosaic Disease of Privet (Ligustrum vulgare) in Europe

Wild plants serve as a large reservoir of known and yet-unknown viruses and as a source of viral pathogens of cultivated plants. Yellow mosaic disease of forest shrub Ligustrum vulgare (privet) was recurrently observed in Europe for more than 100 years. Using a universal virus identification approach based on deep sequencing and de novo assembly of viral small interfering (si)RNAs we identified a causative agent of this disease in Switzerland and reconstructed its complete 3-segmented RNA genome. Notably, a short 3'-terminal common region (CR) attached to each segment via a ∼53-71 nucleotide poly(A) tract, as determined by RT-PCR sequencing, was initially identified as an orphan siRNA contig with conserved tRNA-like secondary structure. Phylogenomic analysis classified this virus as a novel member in the genus Hordeivirus of family Virgaviridae, which we named ligustrum mosaic virus (LigMV). Similar to other hordeiviruses, LigMV formed rod-shape virions (visualized by electron microscopy), was transmitted through seeds and could also be mechanically transmitted to herbaceous hosts Chenopodium quinoa and Nicotiana benthamiana. Blot hybridization analysis identified genomic and subgenomic RNAs, sharing the 3'-CR and likely serving as monocistronic mRNAs for seven evolutionarily-conserved viral proteins including two subunits of viral RNA-dependent RNA polymerase, coat protein, triple gene block proteins mediating viral movement and cysteine-rich suppressor of RNA silencing. Analysis of size, polarity, and hotspot profiles of viral siRNAs suggested that they are produced by the plant antiviral Dicer-like (DCL) proteins DCL2 and DCL4 processing double-stranded intermediates of genomic RNA replication. Whole genome sequencing of French and Austrian isolates of LigMV revealed its genetic stability over a wide geographic range (>99% nucleotide identity to Swiss isolates and each other), suggesting its persistence and spread in Europe via seed dispersal.

First historical genome of a crop bacterial pathogen from herbarium specimen: Insights into citrus canker emergence

Over the past decade, ancient genomics has been used in the study of various pathogens. In this context, herbarium specimens provide a precious source of dated and preserved DNA material, enabling a better understanding of plant disease emergences and pathogen evolutionary history. We report here the first historical genome of a crop bacterial pathogen, Xanthomonas citri pv. citri (Xci), obtained from an infected herbarium specimen dating back to 1937. Comparing the 1937 genome within a large set of modern genomes, we reconstructed their phylogenetic relationships and estimated evolutionary parameters using Bayesian tip-calibration inferences. The arrival of Xci in the South West Indian Ocean islands was dated to the 19th century, probably linked to human migrations following slavery abolishment. We also assessed the metagenomic community of the herbarium specimen, showed its authenticity using DNA damage patterns, and investigated its genomic features including functional SNPs and gene content, with a focus on virulence factors.

A Primer on the Analysis of High-Throughput Sequencing Data for Detection of Plant Viruses

High-throughput sequencing (HTS) technologies have become indispensable tools assisting plant virus diagnostics and research thanks to their ability to detect any plant virus in a sample without prior knowledge. As HTS technologies are heavily relying on bioinformatics analysis of the huge amount of generated sequences, it is of utmost importance that researchers can rely on efficient and reliable bioinformatic tools and can understand the principles, advantages, and disadvantages of the tools used. Here, we present a critical overview of the steps involved in HTS as employed for plant virus detection and virome characterization. We start from sample preparation and nucleic acid extraction as appropriate to the chosen HTS strategy, which is followed by basic data analysis requirements, an extensive overview of the in-depth data processing options, and taxonomic classification of viral sequences detected. By presenting the bioinformatic tools and a detailed overview of the consecutive steps that can be used to implement a well-structured HTS data analysis in an easy and accessible way, this paper is targeted at both beginners and expert scientists engaging in HTS plant virome projects.

Resurrection of a Viral Internal Ribosome Entry Site from a 700 Year Old Ancient Northwest Territories Cripavirus

The dicistrovirus intergenic region internal ribosome entry site (IGR IRES) uses an unprecedented, streamlined mechanism whereby the IRES adopts a triple-pseudoknot (PK) structure to directly bind to the conserved core of the ribosome and drive translation from a non-AUG codon. The origin of this IRES mechanism is not known. Previously, a partial fragment of a divergent dicistrovirus RNA genome, named ancient Northwest territories cripavirus (aNCV), was extracted from 700-year-old caribou feces trapped in a subarctic ice patch. The aNCV IGR sequence adopts a secondary structure similar to contemporary IGR IRES structures, however, there are subtle differences including 105 nucleotides upstream of the IRES of unknown function. Using filter binding assays, we showed that the aNCV IRES could bind to purified ribosomes, and toeprinting analysis pinpointed the start site at a GCU alanine codon adjacent to PKI. Using a bicistronic reporter RNA, the aNCV IGR can direct translation in vitro in a PKI-dependent manner. Lastly, a chimeric infectious clone swapping in the aNCV IRES supported translation and virus infection. The characterization and resurrection of a functional IGR IRES from a divergent 700-year-old virus provides a historical framework for the importance of this viral translational mechanism.

Next-Generation Sequencing and the CRISPR-Cas Nexus: A Molecular Plant Virology Perspective

In recent years, next-generation sequencing (NGS) and contemporary Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR-associated (Cas) technologies have revolutionized the life sciences and the field of plant virology. Both these technologies offer an unparalleled platform for sequencing and deciphering viral metagenomes promptly. Over the past two decades, NGS technologies have improved enormously and have impacted plant virology. NGS has enabled the detection of plant viruses that were previously undetectable by conventional approaches, such as quarantine and archeological plant samples, and has helped to track the evolutionary footprints of viral pathogens. The CRISPR-Cas-based genome editing (GE) and detection techniques have enabled the development of effective approaches to virus resistance. Different versions of CRISPR-Cas have been employed to successfully confer resistance against diverse plant viruses by directly targeting the virus genome or indirectly editing certain host susceptibility factors. Applications of CRISPR-Cas systems include targeted insertion and/or deletion, site-directed mutagenesis, induction/expression/repression of the gene(s), epigenome re-modeling, and SNPs detection. The CRISPR-Cas toolbox has been equipped with precision GE tools to engineer the target genome with and without double-stranded (ds) breaks or donor templates. This technique has also enabled the generation of transgene-free genetically engineered plants, DNA repair, base substitution, prime editing, detection of small molecules, and biosensing in plant virology. This review discusses the utilities, advantages, applications, bottlenecks of NGS, and CRISPR-Cas in plant virology.

Ancient microRNA profiles of a 14,300-year-old canid samples confirm taxonomic origin and give glimpses into tissue-specific gene regulation from the Pleistocene

DNA sequencing is the current key technology for historic or ancient biological samples and has led to many exciting discoveries in the field of paleogenomics. However, functional insights into tissue identity, cellular composition or gene regulation cannot be gained from DNA. Recent analyses have shown that, under favorable conditions, RNA can also be sequenced from ancient samples, enabling studies at the transcriptomic and regulatory level. Analyzing ancient RNA data from a Pleistocene canid, we find hundreds of intact microRNAs that are taxonomically informative, show tissue-specificity and have functionally predictive characteristics. With an extraordinary age of 14,300 years, these microRNA sequences are by far the oldest ever reported. The authenticity of the sequences is further supported by a) the presence of canid / Caniformia-specific sequences that never evolved outside of this clade, b) tissue-specific expression patterns (cartilage, liver and muscle) that resemble those of modern dogs and c) RNA damage patterns that are clearly distinct from those of fresh samples. By performing computational microRNA-target enrichment analyses on the ancient sequences, we predict microRNA functions consistent with their tissue pattern of expression. For instance, we find a liver-specific microRNA that regulates carbohydrate metabolism and starvation responses in canids. In summary, we show that straightforward paleotranscriptomic microRNA analyses can give functional glimpses into tissue identity, cellular composition and gene regulatory activity of ancient samples and biological processes that took place in the Pleistocene, thus holding great promise for deeper insights into gene regulation in extinct animals based on ancient RNA sequencing. .

Variola virus genome sequenced from an eighteenth-century museum specimen supports the recent origin of smallpox

Smallpox, caused by the variola virus (VARV), was a highly virulent disease with high mortality rates causing a major threat for global human health until its successful eradication in 1980. Despite previously published historic and modern VARV genomes, its past dissemination and diversity remain debated. To understand the evolutionary history of VARV with respect to historic and modern VARV genetic variation in Europe, we sequenced a VARV genome from a well-described eighteenth-century case from England (specimen P328). In our phylogenetic analysis, the new genome falls between the modern strains and another historic strain from Lithuania, supporting previous claims of larger diversity in early modern Europe compared to the twentieth century. Our analyses also resolve a previous controversy regarding the common ancestor between modern and historic strains by confirming a later date around the seventeenth century. Overall, our results point to the benefit of historic genomes for better resolution of past VARV diversity and highlight the value of such historic genomes from around the world to further understand the evolutionary history of smallpox as well as related diseases. This article is part of the theme issue 'Insights into health and disease from ancient biomolecules'.

Brachypodium and plant viruses: entwined tools for discovery

In just a decade, Brachypodium distachyon (Brachypodium) has fulfilled its initial promise as a key tool for realizing new strategies for understanding host and pathogen biology during virus infections of the Poaceae. For this Tansley Insight, I have identified four areas - from the laboratory to the field - that may be particularly fruitful to explore, with a particular focus on Brachypodium-virus infections. These focus areas include: mechanisms of RNA modification of host plants and viruses; coevolution of virus-host interactions; viruses as tools of discovery; and how to explicate the complex outcomes during multivirus infections. Here, I broadly frame our current knowledge of Brachypodium-virus interactions and how these findings may inform virus studies of grasses in the laboratory, field and natural settings.

A synthesis of virus-vector associations reveals important deficiencies in studies on host and vector manipulation by plant viruses

Plant viruses face many challenges in agricultural environments. Although crop fields appear to be abundant resources for these pathogens, it may be difficult for viruses to "escape" from crop environments prior to host senescence or harvesting. One way for viruses to increase the odds of persisting outside of agricultural fields across seasons is by evolving traits that increase transmission opportunities between crops and wild plant communities. There is accumulating evidence that some viruses can achieve this by manipulating crop plant phenotypes in ways that enhance transmission by vectors. Putative manipulations occur through alteration of plant cues (color, size, texture, foliar volatiles, in-leaf metabolites, defenses, and leaf cuticles) that mediate vector orientation, feeding, and dispersal behaviors. Virus effects on host phenotypes are not uniform but appear to exhibit convergence depending on virus traits underlying transmission, particularly the duration of probing and feeding required to acquire and inoculate distinct types of plant viruses. This shared congruence in manipulation strategies and mechanisms across divergent virus lineages suggests that such effects may be adaptive. To discern if this is the case, researchers must consider molecular and environmental constraints on virus evolution, including those imposed by insect vectors from organismal to landscape scales. In this review, we synthesize applied research on vector-borne virus transmission in laboratory and field settings to identify the main factors determining transmission opportunities for plant viruses, and thus, selection pressure to evolve manipulative traits. We then examine these outputs in the context of studies reporting putative instances of plant virus manipulation. Our synthesis reveals important disconnects between virus manipulation studies and actual selection pressures imposed by vectors in real-world contexts.

Ancient Plant Genomics in Archaeology, Herbaria, and the Environment

The ancient DNA revolution of the past 35 years has driven an explosion in the breadth, nuance, and diversity of questions that are approachable using ancient biomolecules, and plant research has been a constant, indispensable facet of these developments. Using archaeological, paleontological, and herbarium plant tissues, researchers have probed plant domestication and dispersal, plant evolution and ecology, paleoenvironmental composition and dynamics, and other topics across related disciplines. Here, we review the development of the ancient DNA discipline and the role of plant research in its progress and refinement. We summarize our understanding of long-term plant DNA preservation and the characteristics of degraded DNA. In addition, we discuss challenges in ancient DNA recovery and analysis and the laboratory and bioinformatic strategies used to mitigate them. Finally, we review recent applications of ancient plant genomic research.

A new method for inferring timetrees from temporally sampled molecular sequences

Pathogen timetrees are phylogenies scaled to time. They reveal the temporal history of a pathogen spread through the populations as captured in the evolutionary history of strains. These timetrees are inferred by using molecular sequences of pathogenic strains sampled at different times. That is, temporally sampled sequences enable the inference of sequence divergence times. Here, we present a new approach (RelTime with Dated Tips [RTDT]) to estimating pathogen timetrees based on a relative rate framework underlying the RelTime approach that is algebraic in nature and distinct from all other current methods. RTDT does not require many of the priors demanded by Bayesian approaches, and it has light computing requirements. In analyses of an extensive collection of computer-simulated datasets, we found the accuracy of RTDT time estimates and the coverage probabilities of their confidence intervals (CIs) to be excellent. In analyses of empirical datasets, RTDT produced dates that were similar to those reported in the literature. In comparative benchmarking with Bayesian and non-Bayesian methods (LSD, TreeTime, and treedater), we found that no method performed the best in every scenario. So, we provide a brief guideline for users to select the most appropriate method in empirical data analysis. RTDT is implemented for use via a graphical user interface and in high-throughput settings in the newest release of cross-platform MEGA X software, freely available from http://www.megasoftware.net.

Pathogen timetrees trace the origins and evolutionary histories of strains in populations, hosts, and outbreaks. The tips of these molecular phylogenies often contain sampling time information because the sequences were generally obtained at different times during the disease outbreaks and propagation. We have developed a new method for inferring divergence times and confidence intervals for phylogenies with tip dates. The new Relative Times with Dated Tips (RTDT) methods showed excellent performance in the analysis of computer-simulated datasets, producing similar or better results in several evolutionary scenarios as compared to other fast, non-Bayesian methods. The new method is available in the cross-platform MEGA software package (version 10.1 and higher) that provides a graphical user interface and allows usage via a command line in scripting and high throughput analysis (www.megasoftware.net).

Plant virome reconstruction and antiviral RNAi characterization by deep sequencing of small RNAs from dried leaves

In plants, RNA interference (RNAi) generates small interfering (si)RNAs from entire genomes of viruses, satellites and viroids. Therefore, deep small (s)RNA sequencing is a universal approach for virome reconstruction and RNAi characterization. We tested this approach on dried barley leaves from field surveys. Illumina sequencing of sRNAs from 2 plant samples identified in both plants Hordeum vulgare endornavirus (HvEV) and barley yellow mosaic bymovirus (BaYMV) and, additionally in one plant, a novel strain of Japanese soil-borne wheat mosaic furovirus (JSBWMV). De novo and reference-based sRNA assembly yielded complete or near-complete genomic RNAs of these viruses. While plant sRNAs showed broad size distribution, viral sRNAs were predominantly 21 and 22 nucleotides long with 5′-terminal uridine or adenine, and were derived from both genomic strands. These bona fide siRNAs are presumably processed from double-stranded RNA precursors by Dicer-like (DCL) 4 and DCL2, respectively, and associated with Argonaute 1 and 2 proteins. For BaYMV (but not HvEV, or JSBWMV), 24-nucleotide sRNAs represented the third most abundant class, suggesting DCL3 contribution to anti-bymovirus defence. Thus, viral siRNAs are well preserved in dried leaf tissues and not contaminated by non-RNAi degradation products, enabling both complete virome reconstruction and inference of RNAi components mediating antiviral defense.

Phylogeography of Lassa Virus in Nigeria

Lassa virus is the causative agent of Lassa fever, a viral hemorrhagic fever with a case fatality rate of approximately 30% in Africa. Previous studies disclosed a geographical pattern in the distribution of Lassa virus strains and a westward movement of the virus across West Africa during evolution. Our study provides a deeper understanding of the geography of genetic lineages and sublineages of the virus in Nigeria. In addition, we modeled how the virus spread in the country. This knowledge allows us to predict into which geographical areas the virus might spread in the future and prioritize areas for Lassa fever surveillance. Our study not only aimed to generate Lassa virus sequences from across Nigeria but also to isolate and conserve the respective viruses for future research. Both isolates and sequences are important for the development and evaluation of medical countermeasures to treat and prevent Lassa fever, such as diagnostics, therapeutics, and vaccines.

Lassa virus is genetically diverse with several lineages circulating in West Africa. This study aimed at describing the sequence variability of Lassa virus across Nigeria and inferring its spatiotemporal evolution. We sequenced and isolated 77 Lassa virus strains from 16 Nigerian states. The final data set, including previous works, comprised metadata and sequences of 219 unique strains sampled between 1969 and 2018 in 22 states. Most of this data originated from Lassa fever patients diagnosed at Irrua Specialist Teaching Hospital, Edo State, Nigeria. The majority of sequences clustered with the main Nigerian lineages II and III, while a few sequences formed a new cluster related to Lassa virus strains from Hylomyscus pamfi. Within lineages II and III, seven and five sublineages, respectively, were distinguishable. Phylogeographic analysis suggests an origin of lineage II in the southeastern part of the country around Ebonyi State and a main vector of dispersal toward the west across the Niger River, through Anambra, Kogi, Delta, and Edo into Ondo State. The frontline of virus dispersal appears to be in Ondo. Minor vectors are directed northeast toward Taraba and Adamawa and south toward Imo and Rivers. Lineage III might have spread from northern Plateau State into Kaduna, Nasarawa, Federal Capital Territory, and Bauchi. One sublineage moved south and crossed the Benue River into Benue State. This study provides a geographic mapping of lineages and phylogenetic clusters in Nigeria at a higher resolution. In addition, we estimated the direction and time frame of virus dispersal in the country.

IMPORTANCE Lassa virus is the causative agent of Lassa fever, a viral hemorrhagic fever with a case fatality rate of approximately 30% in Africa. Previous studies disclosed a geographical pattern in the distribution of Lassa virus strains and a westward movement of the virus across West Africa during evolution. Our study provides a deeper understanding of the geography of genetic lineages and sublineages of the virus in Nigeria. In addition, we modeled how the virus spread in the country. This knowledge allows us to predict into which geographical areas the virus might spread in the future and prioritize areas for Lassa fever surveillance. Our study not only aimed to generate Lassa virus sequences from across Nigeria but also to isolate and conserve the respective viruses for future research. Both isolates and sequences are important for the development and evaluation of medical countermeasures to treat and prevent Lassa fever, such as diagnostics, therapeutics, and vaccines.

Ancient RNA from Late Pleistocene permafrost and historical canids shows tissue-specific transcriptome survival

While sequencing ancient DNA (aDNA) from archaeological material is now commonplace, very few attempts to sequence ancient transcriptomes have been made, even from typically stable deposition environments such as permafrost. This is presumably due to assumptions that RNA completely degrades relatively quickly, particularly when dealing with autolytic, nuclease-rich mammalian tissues. However, given the recent successes in sequencing ancient RNA (aRNA) from various sources including plants and animals, we suspect that these assumptions may be incorrect or exaggerated. To challenge the underlying dogma, we generated shotgun RNA data from sources that might normally be dismissed for such study. Here, we present aRNA data generated from two historical wolf skins, and permafrost-preserved liver tissue of a 14,300-year-old Pleistocene canid. Not only is the latter the oldest RNA ever to be sequenced, but it also shows evidence of biologically relevant tissue specificity and close similarity to equivalent data derived from modern-day control tissue. Other hallmarks of RNA sequencing (RNA-seq) data such as exon-exon junction presence and high endogenous ribosomal RNA (rRNA) content confirms our data’s authenticity. By performing independent technical library replicates using two high-throughput sequencing platforms, we show not only that aRNA can survive for extended periods in mammalian tissues but also that it has potential for tissue identification. aRNA also has possible further potential, such as identifying in vivo genome activity and adaptation, when sequenced using this technology.

Ancient DNA is known to survive in cold environments for tens of millennia, but it is assumed that ancient RNA could not persist in such a way due to its relative instability. However, this study shows that under permafrost conditions, ancient RNA can survive well enough to show tissue specificity even in mammalian soft tissues.

Modeling of Mutational Events in the Evolution of Viruses

Diverse studies of viral evolution have led to the recognition that the evolutionary rates of viral taxa observed are dependent on the time scale being investigated—with short-term studies giving fast substitution rates, and orders of magnitude lower rates for deep calibrations. Although each of these factors may contribute to this time dependent rate phenomenon, a more fundamental cause should be considered. We sought to test computationally whether the basic phenomena of virus evolution (mutation, replication, and selection) can explain the relationships between the evolutionary and phylogenetic distances. We tested, by computational inference, the hypothesis that the phylogenetic distances between the pairs of sequences are functions of the evolutionary path lengths between them. A Basic simulation revealed that the relationship between simulated genetic and mutational distances is non-linear, and can be consistent with different rates of nucleotide substitution at different depths of branches in phylogenetic trees.

The origin of Oxalis corniculata L

Background

Oxalis corniculata L. is a weed with a world-wide distribution and unknown origin. Though it belongs to a section of the genus from South America, the evidence that this species came from there is weak.

Methods

We reviewed the evidence for the origin of O. corniculata using herbarium specimens, historic literature and archaeobotanical research. We also summarized ethnobotanical literature to understand where this species is most used by humans as a medicine.

Results

Despite numerous claims that it is native to Europe there is no strong evidence that O. corniculata occurred in Europe before the 15th century. Nor is there reliable evidence that it occurred in North or South America before the 19th century. However, there is direct archaeobotanical evidence of it occurring in south–east Asia at least 5,000 years ago. There is also evidence from historic literature and archaeobotany that it reached Polynesia before European expeditions explored these islands. Examination of the traditional use of O. corniculata demonstrates that is most widely used as a medicine in south–east Asia, which, while circumstantial, also points to a long association with human culture in this area.

Discussion

The most likely origin for O. corniculata is south–east Asia. This is consistent with a largely circum-Pacific distribution of section Corniculatae of Oxalis. Nevertheless, it is likely that O. corniculata spread to Europe and perhaps Polynesia before the advent of the modern era through trade routes at that time.

Paleogenomics: reconstruction of plant evolutionary trajectories from modern and ancient DNA

How contemporary plant genomes originated and evolved is a fascinating question. One approach uses reference genomes from extant species to reconstruct the sequence and structure of their common ancestors over deep timescales. A second approach focuses on the direct identification of genomic changes at a shorter timescale by sequencing ancient DNA preserved in subfossil remains. Merged within the nascent field of paleogenomics, these complementary approaches provide insights into the evolutionary forces that shaped the organization and regulation of modern genomes and open novel perspectives in fostering genetic gain in breeding programs and establishing tools to predict future population changes in response to anthropogenic pressure and global warming.

A 1,000-Year-Old RNA Virus

Only a few RNA viruses have been discovered from archaeological samples, the oldest dating from about 750 years ago. Using ancient maize cobs from Antelope house, Arizona, dating from ca. 1,000 CE, we discovered a novel plant virus with a double-stranded RNA genome. The virus is a member of the family Chrysoviridae that infect plants and fungi in a persistent manner. The extracted double-stranded RNA from 312 maize cobs was converted to cDNA, and sequences were determined using an Illumina HiSeq 2000. Assembled contigs from many samples showed similarity to Anthurium mosaic-associated virus and Persea americana chrysovirus, putative species in the Chrysovirus genus, and nearly complete genomes were found in three ancient maize samples. We named this new virus Zea mays chrysovirus 1. Using specific primers, we were able to recover sequences of a closely related virus from modern maize and obtained the nearly complete sequences of the three genomic RNAs. Comparing the nucleotide sequences of the three genomic RNAs of the modern and ancient viruses showed 98, 96.7, and 97.4% identities, respectively. Hence, in 1,000 years of maize cultivation, this virus has undergone about 3% divergence.IMPORTANCE A virus related to plant chrysoviruses was found in numerous ancient samples of maize, with nearly complete genomes in three samples. The age of the ancient samples (i.e., about 1,000 years old) was confirmed by carbon dating. Chrysoviruses are persistent plant viruses. They infect their hosts from generation to generation by transmission through seeds and can remain in their hosts for very long time periods. When modern corn samples were analyzed, a closely related chrysovirus was found with only about 3% divergence from the ancient sequences. This virus represents the oldest known plant virus.

Small RNA-Omics for Plant Virus Identification, Virome Reconstruction, and Antiviral Defense Characterization

RNA interference (RNAi)-based antiviral defense generates small interfering RNAs that represent the entire genome sequences of both RNA and DNA viruses as well as viroids and viral satellites. Therefore, deep sequencing and bioinformatics analysis of small RNA population (small RNA-ome) allows not only for universal virus detection and genome reconstruction but also for complete virome reconstruction in mixed infections. Viral infections (like other stress factors) can also perturb the RNAi and gene silencing pathways regulating endogenous gene expression and repressing transposons and host genome-integrated endogenous viral elements which can potentially be released from the genome and contribute to disease. This review describes the application of small RNA-omics for virus detection, virome reconstruction and antiviral defense characterization in cultivated and non-cultivated plants. Reviewing available evidence from a large and ever growing number of studies of naturally or experimentally infected hosts revealed that all families of land plant viruses, their satellites and viroids spawn characteristic small RNAs which can be assembled into contigs of sufficient length for virus, satellite or viroid identification and for exhaustive reconstruction of complex viromes. Moreover, the small RNA size, polarity and hotspot profiles reflect virome interactions with the plant RNAi machinery and allow to distinguish between silent endogenous viral elements and their replicating episomal counterparts. Models for the biogenesis and functions of small interfering RNAs derived from all types of RNA and DNA viruses, satellites and viroids as well as endogenous viral elements are presented and discussed.

Barley RNA viromes in six different geographical regions in Korea

Barley is a kind of cereal grass belonging to the family Poaceae. To examine viruses infecting winter barley in Korea, we carried out a comprehensive study of barley RNA viromes using next-generation sequencing (NGS). A total of 110 barley leaf samples from 17 geographical locations were collected. NGS followed by extensive bioinformatics analyses revealed six different barley viromes: Barley yellow mosaic virus (BaYMV), Barley mild mosaic virus (BaMMV), Barley yellow dwarf virus (BYDV), Hordeum vulgare endornavirus (HvEV), and Barley virus G (BVG). BaYMV and HvEV were identified in all libraries, while other viruses were identified in some specific library. Based on the number of virus-associated reads, BaYMV was a dominant virus infecting winter barley in Korea causing yellow disease symptoms. We obtained nearly complete genomes of six BaYMV isolates and two BaMMV isolates. Phylogenetic analyses indicate that BaYMV and BaMMV were largely grouped based on geographical regions such as Asia and Europe. Single nucleotide polymorphisms analyses suggested that most BaYMV and BaMMV showed strong genetic variations; however, BaYMV isolate Jeonju and BaMMV isolate Gunsan exhibited a few and no SNPs, respectively, suggesting low level of genetic variation. Taken together, this is the first study of barley RNA viromes in Korea.

Comparative performance of the BGISEQ-500 vs Illumina HiSeq2500 sequencing platforms for palaeogenomic sequencing

Ancient DNA research has been revolutionized following development of next-generation sequencing platforms. Although a number of such platforms have been applied to ancient DNA samples, the Illumina series are the dominant choice today, mainly because of high production capacities and short read production. Recently a potentially attractive alternative platform for palaeogenomic data generation has been developed, the BGISEQ-500, whose sequence output are comparable with the Illumina series. In this study, we modified the standard BGISEQ-500 library preparation specifically for use on degraded DNA, then directly compared the sequencing performance and data quality of the BGISEQ-500 to the Illumina HiSeq2500 platform on DNA extracted from 8 historic and ancient dog and wolf samples. The data generated were largely comparable between sequencing platforms, with no statistically significant difference observed for parameters including level (P = 0.371) and average sequence length (P = 0718) of endogenous nuclear DNA, sequence GC content (P = 0.311), double-stranded DNA damage rate (v. 0.309), and sequence clonality (P = 0.093). Small significant differences were found in single-strand DNA damage rate (δS; slightly lower for the BGISEQ-500, P = 0.011) and the background rate of difference from the reference genome (θ; slightly higher for BGISEQ-500, P = 0.012). This may result from the differences in amplification cycles used to polymerase chain reaction–amplify the libraries. A significant difference was also observed in the mitochondrial DNA percentages recovered (P = 0.018), although we believe this is likely a stochastic effect relating to the extremely low levels of mitochondria that were sequenced from 3 of the samples with overall very low levels of endogenous DNA. Although we acknowledge that our analyses were limited to animal material, our observations suggest that the BGISEQ-500 holds the potential to represent a valid and potentially valuable alternative platform for palaeogenomic data generation that is worthy of future exploration by those interested in the sequencing and analysis of degraded DNA.

Molecular analysis of barley stripe mosaic virus isolates differing in their biological properties and the development of reverse transcription loop-mediated isothermal amplification assays for their detection

Barley stripe mosaic virus (BSMV) is an important seed-transmitted pathogen occurring worldwide. Recently, the occurrence of mild BSMV pathotypes has been observed in barley crops in Poland. In this study, the full-length genome sequences of mild and aggressive Polish and German BSMV isolates was established. Phylogenetic and recombination analysis was performed using Polish and other BSMV isolates described to date. The analysis revealed that Polish isolates differed only in 25 nucleotides, which suggests that point mutations might have had a great impact on the biological properties of the virus. The phylogenetic analysis revealed that the closest relationship was that between European and BSMV-CV42, BSMV-ND18 and BSMV-Type isolates, whereas the highest genetic distance was observed for BSMV-Qasr Ibrim and BSMV-China isolates. A recombination event within the αa protein of BSMV-De-M and BSMV-CV42 isolates was also detected. Moreover, a sensitive reverse transcription loop-mediated isothermal amplification (RT-LAMP) method was developed for rapid detection of BSMV isolates. The RT-LAMP assay can be used for routine diagnostics of BSMV in seed and plant material.

Ancient DNA provides evidence of 27,000-year-old papillomavirus infection and long-term codivergence with rodents

The long-term evolutionary history of many viral lineages is poorly understood. Novel sources of ancient DNA combined with phylogenetic analyses can provide insight into the time scale of virus evolution. Here we report viral sequences from ancient North American packrat middens. We screened samples up to 27,000-years old and found evidence of papillomavirus (PV) infection in Neotoma cinerea (Bushy-tailed packrat). Phylogenetic analysis placed the PV sequences in a clade with other previously published PV sequences isolated from rodents. Concordance between the host and virus tree topologies along with a correlation in branch lengths suggests a shared evolutionary history between rodents and PVs. Based on host divergence times, PVs have likely been circulating in rodents for at least 17 million years. These results have implications for our understanding of PV evolution and for further research with ancient DNA from Neotoma middens.

Small RNA Activity in Archeological Barley Shows Novel Germination Inhibition in Response to Environment

The recovery of ancient RNA from archeological material could enable the direct study of microevolutionary processes. Small RNAs are a rich source of information because their small size is compatible with biomolecular preservation, and their roles in gene regulation make them likely foci of evolutionary change. We present here the small RNA fraction from a sample of archeological barley generated using high-throughput sequencing that has previously been associated with localized adaptation to drought. Its microRNA profile is broadly similar to 19 globally distributed modern barley samples with the exception of three microRNAs (miRNA159, miRNA319, and miR396), all of which are known to have variable expression under stress conditions. We also found retrotransposon activity to be significantly reduced in the archeological barley compared with the controls, where one would expect the opposite under stress conditions. We suggest that the archeological barley's conflicting stress signals could be the result of long-term adaptation to its local environment.

A Robust Framework for Microbial Archaeology

Microbial archaeology is flourishing in the era of high-throughput sequencing, revealing the agents behind devastating historical plagues, identifying the cryptic movements of pathogens in prehistory, and reconstructing the ancestral microbiota of humans. Here, we introduce the fundamental concepts and theoretical framework of the discipline, then discuss applied methodologies for pathogen identification and microbiome characterization from archaeological samples. We give special attention to the process of identifying, validating, and authenticating ancient microbes using high-throughput DNA sequencing data. Finally, we outline standards and precautions to guide future research in the field.

Exploiting Genetic Information to Trace Plant Virus Dispersal in Landscapes

During the past decade, knowledge of pathogen life history has greatly benefited from the advent and development of molecular epidemiology. This branch of epidemiology uses information on pathogen variation at the molecular level to gain insights into a pathogen's niche and evolution and to characterize pathogen dispersal within and between host populations. Here, we review molecular epidemiology approaches that have been developed to trace plant virus dispersal in landscapes. In particular, we highlight how virus molecular epidemiology, nourished with powerful sequencing technologies, can provide novel insights at the crossroads between the blooming fields of landscape genetics, phylogeography, and evolutionary epidemiology. We present existing approaches and their limitations and contributions to the understanding of plant virus epidemiology.

Ecological consequences of human niche construction: Examining long-term anthropogenic shaping of global species distributions

The exhibition of increasingly intensive and complex niche construction behaviors through time is a key feature of human evolution, culminating in the advanced capacity for ecosystem engineering exhibited by Homo sapiens A crucial outcome of such behaviors has been the dramatic reshaping of the global biosphere, a transformation whose early origins are increasingly apparent from cumulative archaeological and paleoecological datasets. Such data suggest that, by the Late Pleistocene, humans had begun to engage in activities that have led to alterations in the distributions of a vast array of species across most, if not all, taxonomic groups. Changes to biodiversity have included extinctions, extirpations, and shifts in species composition, diversity, and community structure. We outline key examples of these changes, highlighting findings from the study of new datasets, like ancient DNA (aDNA), stable isotopes, and microfossils, as well as the application of new statistical and computational methods to datasets that have accumulated significantly in recent decades. We focus on four major phases that witnessed broad anthropogenic alterations to biodiversity-the Late Pleistocene global human expansion, the Neolithic spread of agriculture, the era of island colonization, and the emergence of early urbanized societies and commercial networks. Archaeological evidence documents millennia of anthropogenic transformations that have created novel ecosystems around the world. This record has implications for ecological and evolutionary research, conservation strategies, and the maintenance of ecosystem services, pointing to a significant need for broader cross-disciplinary engagement between archaeology and the biological and environmental sciences.

Investigating Gene Function in Cereal Rust Fungi by Plant-Mediated Virus-Induced Gene Silencing

Cereal rust fungi are destructive pathogens, threatening grain production worldwide. Targeted breeding for resistance utilizing host resistance genes has been effective. However, breakdown of resistance occurs frequently and continued efforts are needed to understand how these fungi overcome resistance and to expand the range of available resistance genes. Whole genome sequencing, transcriptomic and proteomic studies followed by genome-wide computational and comparative analyses have identified large repertoire of genes in rust fungi among which are candidates predicted to code for pathogenicity and virulence factors. Some of these genes represent defence triggering avirulence effectors. However, functions of most genes still needs to be assessed to understand the biology of these obligate biotrophic pathogens. Since genetic manipulations such as gene deletion and genetic transformation are not yet feasible in rust fungi, performing functional gene studies is challenging. Recently, Host-induced gene silencing (HIGS) has emerged as a useful tool to characterize gene function in rust fungi while infecting and growing in host plants. We utilized Barley stripe mosaic virus-mediated virus induced gene silencing (BSMV-VIGS) to induce HIGS of candidate rust fungal genes in the wheat host to determine their role in plant-fungal interactions. Here, we describe the methods for using BSMV-VIGS in wheat for functional genomics study in cereal rust fungi.

Deep sequencing for discovery and evolutionary analysis of plant viruses

The advent of next generation sequencing (NGS), or deep sequencing, has allowed great advances to be made in discovery, diagnostics, and evolutionary studies in plant viruses. Various methods have been used for enrichment for virus-specific nucleic acids, each of which have some drawbacks. Many novel viruses have been discovered in plants by NGS technologies, and there is a good deal of promise for more comprehensive studies in virus evolution. However, each aspect of using NGS has its caveats that need to be considered, and there is still a need for better tools of analysis, as well as method for validation of sequence variation.

Next-Generation Sequencing and Genome Editing in Plant Virology

Next-generation sequencing (NGS) has been applied to plant virology since 2009. NGS provides highly efficient, rapid, low cost DNA, or RNA high-throughput sequencing of the genomes of plant viruses and viroids and of the specific small RNAs generated during the infection process. These small RNAs, which cover frequently the whole genome of the infectious agent, are 21-24 nt long and are known as vsRNAs for viruses and vd-sRNAs for viroids. NGS has been used in a number of studies in plant virology including, but not limited to, discovery of novel viruses and viroids as well as detection and identification of those pathogens already known, analysis of genome diversity and evolution, and study of pathogen epidemiology. The genome engineering editing method, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system has been successfully used recently to engineer resistance to DNA geminiviruses (family, Geminiviridae) by targeting different viral genome sequences in infected Nicotiana benthamiana or Arabidopsis plants. The DNA viruses targeted include tomato yellow leaf curl virus and merremia mosaic virus (begomovirus); beet curly top virus and beet severe curly top virus (curtovirus); and bean yellow dwarf virus (mastrevirus). The technique has also been used against the RNA viruses zucchini yellow mosaic virus, papaya ringspot virus and turnip mosaic virus (potyvirus) and cucumber vein yellowing virus (ipomovirus, family, Potyviridae) by targeting the translation initiation genes eIF4E in cucumber or Arabidopsis plants. From these recent advances of major importance, it is expected that NGS and CRISPR-Cas technologies will play a significant role in the very near future in advancing the field of plant virology and connecting it with other related fields of biology.

Phosphorylation of TGB1 by protein kinase CK2 promotes barley stripe mosaic virus movement in monocots and dicots

The barley stripe mosaic virus (BSMV) triple gene block 1 (TGB1) protein is required for virus cell-to-cell movement. However, little information is available about how these activities are regulated by post-translational modifications. In this study, we showed that the BSMV Xinjiang strain TGB1 (XJTGB1) is phosphorylated in vivo and in vitro by protein kinase CK2 from barley and Nicotiana benthamiana. Liquid chromatography tandem mass spectrometry analysis and in vitro phosphorylation assays demonstrated that Thr-401 is the major phosphorylation site of the XJTGB1 protein, and suggested that a Thr-395 kinase docking site supports Thr-401 phosphorylation. Substitution of Thr-395 with alanine (T395A) only moderately impaired virus cell-to-cell movement and systemic infection. In contrast, the Thr-401 alanine (T401A) virus mutant was unable to systemically infect N. benthamiana but had only minor effects in monocot hosts. Substitution of Thr-395 or Thr-401 with aspartic acid interfered with monocot and dicot cell-to-cell movement and the plants failed to develop systemic infections. However, virus derivatives with single glutamic acid substitutions at Thr-395 and Thr-401 developed nearly normal systemic infections in the monocot hosts but were unable to infect N. benthamiana systemically, and none of the double mutants was able to infect dicot and monocot hosts. The mutant XJTGB1T395A/T401A weakened in vitro interactions between XJTGB1 and XJTGB3 proteins but had little effect on XJTGB1 RNA-binding ability. Taken together, our results support a critical role of CK2 phosphorylation in the movement of BSMV in monocots and dicots, and provide new insights into the roles of phosphorylation in TGB protein functions.

Using archaeogenomic and computational approaches to unravel the history of local adaptation in crops

Our understanding of the evolution of domestication has changed radically in the past 10 years, from a relatively simplistic rapid origin scenario to a protracted complex process in which plants adapted to the human environment. The adaptation of plants continued as the human environment changed with the expansion of agriculture from its centres of origin. Using archaeogenomics and computational models, we can observe genome evolution directly and understand how plants adapted to the human environment and the regional conditions to which agriculture expanded. We have applied various archaeogenomics approaches as exemplars to study local adaptation of barley to drought resistance at Qasr Ibrim, Egypt. We show the utility of DNA capture, ancient RNA, methylation patterns and DNA from charred remains of archaeobotanical samples from low latitudes where preservation conditions restrict ancient DNA research to within a Holocene timescale. The genomic level of analyses that is now possible, and the complexity of the evolutionary process of local adaptation means that plant studies are set to move to the genome level, and account for the interaction of genes under selection in systems-level approaches. This way we can understand how plants adapted during the expansion of agriculture across many latitudes with rapidity.