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Biological control, or biocontrol, is the exploitation of living agents (incl. viruses) to combat pestilential organisms (incl. pathogens, pests, and weeds) for diverse purposes to provide human benefits. Thus, during the last century the practices and concepts involved have evolved in separate streams associated with distinct scientific and taxonomic disciplines. In parallel developments, there have been increasing references to biological control in industrial contexts and legislation, resulting in conceptual and terminological disintegration. The aim of this paper is to provide a global conceptual and terminological platform that facilitates future development of the field. We review use of previously suggested terms in key fields (e.g., phytopathology, entomology, and weed science), eliminate redundant terminology, identify three principles that should underpin the concept, and then present a new framework for biological control, rooted in seminal publications. The three principles establish that (1) only living agents can mediate biological control, (2) biological control always targets a pest, directly or indirectly, and (3) all biocontrol methods can be classified in four main categories depending on whether resident agents are utilized, with or without targeted human intervention (conservation biological control and natural biological control, respectively) or agents are added for permanent or temporary establishment (classical biological control and augmentative biological control, respectively). Correct identification of what is, and is not, biological control can help efforts to understand and optimize biological pest control for human and environmental benefits. The new conceptual framework may contribute to more uniform and appropriate regulatory approaches to biological control, and more efficient authorization and application of biocontrol products.

Chrysanthemum virus B encodes a multifunctional p12 protein that acts as a transcriptional activator in the nucleus and as a suppressor of RNA silencing in the cytoplasm. Here, we investigated the impact of p12 on accumulation of major classes of small RNAs (sRNAs). The results show dramatic changes in the sRNA profiles characterised by an overall reduction in sRNA accumulation, changes in the pattern of size distribution of canonical siRNAs and in the ratio between sense and antisense strands, lower abundance of siRNAs with a U residue at the 5′-terminus, and changes in the expression of certain miRNAs, most of which were downregulated. Electronic supplementary material The online version of this article (10.1007/s00705-020-04832-y) contains supplementary material, which is available to authorized users.

The work of LT, GC, SJ and AR is funded by the Scottish Government’s Rural and Environmental Science and Analytical Services (RESAS) Division, PH by the BBSRC (grant BB/M024911/1) and The Royal Society and EIS by the Swedish Research Council Formas and the Carl Tryggers Foundation. Virus movement proteins facilitate virus entry into the vascular system to initiate systemic infection. The potato mop-top virus (PMTV) movement protein, TGB1, is involved in long-distance movement of both viral ribonucleoprotein complexes and virions. Here, our analysis of TGB1 interactions with host Nicotiana benthamiana proteins revealed an interaction with a member of the heavy metal-associated isoprenylated plant protein family, HIPP26, which acts as a plasma membrane-to-nucleus signal during abiotic stress. We found that knockdown of NbHIPP26 expression inhibited virus long-distance movement but did not affect cell-to-cell movement. Drought and PMTV infection up-regulated NbHIPP26 gene expression, and PMTV infection protected plants from drought. In addition, NbHIPP26 promoter-reporter fusions revealed vascular tissue-specific expression. Mutational and biochemical analyses indicated that NbHIPP26 subcellular localization at the plasma membrane and plasmodesmata was mediated by lipidation (S-acylation and prenylation), as nonlipidated NbHIPP26 was predominantly in the nucleus. Notably, coexpression of NbHIPP26 with TGB1 resulted in a similar nuclear accumulation of NbHIPP26. TGB1 interacted with the carboxyl-terminal CVVM (prenyl) domain of NbHIPP26, and bimolecular fluorescence complementation revealed that the TGB1-HIPP26 complex localized to microtubules and accumulated in the nucleolus, with little signal at the plasma membrane or plasmodesmata. These data support a mechanism where interaction with TGB1 negates or reverses NbHIPP26 lipidation, thus releasing membrane-associated NbHIPP26 and redirecting it via microtubules to the nucleus, thereby activating the drought stress response and facilitating virus long-distance movement. Postprint

Virus research has advanced significantly since the discovery of the tobacco mosaic virus (TMV), the characterization of its infection mechanisms and the factors that determine their pathogenicity. However, most viral research has focused on pathogenic viruses to humans, animals and plants, which represent only a small fraction in the virosphere. As a result, the role of most viral genes, and the mechanisms of coevolution between mutualistic viruses, their host and their environment, beyond pathogenicity, remain poorly understood. This review focuses on general aspects of viruses that interact with extremophile organisms, characteristics and examples of mechanisms of adaptation. Finally, this review provides an overview on how knowledge of extremophile viruses sheds light on the application of new tools of relevant use in modern molecular biology, discussing their value in a biotechnological context.

Potato is the fourth most important crop worldwide that is used as a staple food, after rice, wheat and maize. The crop can be affected by a large number of pathogens, including fungi, oomycetes, bacteria and viruses. Diseases caused by viruses are among the most important factors contributing to reduced quality and yield of the crop. Potato mop-top virus (genus Pomovirus) induces necrotic flecks in the tuber flesh and skin of potato in temperate countries. Spongospora subterranea is the vector of PMTV. Both the virus and its vector cause disease in potato. In Colombia, PMTV has been detected throughout the country together with a novel pomo-like virus in the centre (Cundinamarca and Boyacá) and south west (Nariño) of the country. We studied the molecular and biological characteristics of this novel virus. Its genome resembles those of members of the genus Pomovirus, and it is closely related to PMTV. It induces mild systemic symptoms in Nicotiana benthamiana (mosaic, branch curling), but no symptoms in N. tabacum, N. debneyi and Chenopodium amaranticolor. The proposed name for the virus is "Colombian potato soil-borne virus" (CPSbV). Additionally, another pomo-like virus was identified in Nariño. This virus induces severe systemic stem declining and mild mosaic in N. benthamiana. The tentative name "soil-borne virus 2" (SbV2) is proposed for this virus. No vectors have been identified for these viruses despite several attempts. This work focused on the characterisation of CPSbV. The risk posed by these viruses if they are introduced into new territories is discussed.

Potato mop-top virus (PMTV) causes necrotic flecks inside and on tubers in temperate countries. In South America, these symptoms have not been observed, although the presence of the virus has been confirmed in the Andes and in Central America. To characterize PMTV isolates from the Andes, soil samples were taken from the main potato-producing regions in Colombia and virus was recovered by planting Nicotiana benthamiana as bait plants. The complete genomes of five isolates were sequenced and three of the isolates were inoculated to four different indicator plants. Based on sequence comparisons, three types of RNA-CP (RNA2) and RNA-TGB (RNA3) were found. The isolates from the centre of the country (CO3 and CO4) were similar to isolates from Europe. The genomes of CO1, CO2 and CO5 differ from other PMTV isolates, placing them in a separate clade in phylogenetic trees. The three Colombian isolates (CO1, CO2 and CO5) only induced slightly different symptoms in the indicator plants. However, the isolate from the northwest of the country (CO1) induced stronger symptoms in N. benthamiana including severe stunting. A correlation between the genotype of the isolates and the symptoms they induced on indicator plants was not found.

Summary The evolutionary divergence of Potato mop‐top virus (PMTV), a tri‐partite, single‐stranded RNA virus, is exceptionally low, based on the analysis of sequences obtained from isolates from Europe, Asia and North America. In general, RNA viruses exist as dynamic populations of closely related and recombinant genomes that are subjected to continuous genetic variation. The reason behind the low genetic variation of PMTV remains unclear. The question remains as to whether the low variability is a shared property of all PMTV isolates or is a result of the limited number of isolates characterized so far. We hypothesized that higher divergence of the virus might exist in the Andean regions of South America, the centre of potato domestication. Here, we report high variability of PMTV isolates collected from 12 fields in three locations in the Andean region of Peru. To evaluate PMTV genetic variation in Peru, we generated full‐length cDNA clones, which allowed reliable comparative molecular and pathobiological characterization of individual isolates. We found significant divergence of the CP‐RT and 8K sequences. The 8K cistron, which encodes a viral suppressor of RNA silencing, was found to be under diversifying selection. Phylogenetic analysis determined that, based on the CP‐RT sequence, all PMTV isolates could be categorized into three separate lineages (clades). Moreover, we found evidence for recombination between two clades. Using infectious cDNA clones of the representatives of these two clades, as well as reassortants for the RNA‐CP genomic component, we determined the pathobiological differences between the lineages, which we coined as S (for severe) and M (for mild) types. Interestingly, all isolates characterized previously (from Europe, Asia and North America) fall into the S‐type clade, whereas most of the Peruvian isolates belong to the M‐type. Taken together, our results support the notion of the single introduction of PMTV from the centre of potato origin to Europe, and subsequent spread of the S‐type into Asia and USA. This is also supported by the suggested novel classification of isolates based on genetic constellations.

Recent advances in high-throughput sequencing technologies and bioinformatics have generated huge new opportunities for discovering and diagnosing plant viruses and viroids. Plant virology has undoubtedly benefited from these new methodologies, but at the same time, faces now substantial bottlenecks, namely the biological characterization of the newly discovered viruses and the analysis of their impact at the biosecurity, commercial, regulatory, and scientific levels. This paper proposes a scaled and progressive scientific framework for efficient biological characterization and risk assessment when a previously known or a new plant virus is detected by next generation sequencing (NGS) technologies. Four case studies are also presented to illustrate the need for such a framework, and to discuss the scenarios.

Meteorites have captured our fascination since our early history – they have evoked awe, fear, an irresistible curiosity, and numerous lively debates. Former historians have indicated that many of the ancient cultures and civilizations in Europe, Africa, Asia, the Inuit, and the native Indians in America regarded both the meteorite and the location of their fall as sacred. Thus, they used the meteorites as religious objects or for craft design like jewelry, weapons, or even practical things like tools and horse shoes. Today, meteorites continue to capture our fascination through popular cultural formats such as science fiction and also as a scientific window that reveals the secrets of the Solar System formation. Within academia, meteorites have always fomented keen scientific debate. It was not until the early nineteenth century that the cosmic origin of meteorites, i.e., being truly not tellurian, was approved by the scientific community after the late eighteenth-century work of Ernst F. Chladni (1794). This implied for the first time that there are other smaller bodies in the sky besides the Moon. After this, several other lively debates followed on controversial findings and hypotheses around the role of meteorites in the universe and for the evolutionary course of life on Earth, often in connection with the profound difficulties to approach this subject in an adequate scientific way. Principally the different types of meteorites (asteroids, meteors, etc.) can be viewed as a most extreme or exotic substrate, habitat, and transport mode of chemicals and possibly even of cell-based life forms for several reasons: (i) They have experienced a remarkable history since their origin as condensates from the Solar Nebula, more or less metamorphosed or molten fragments of asteroids, or rocks from Mars or our Moon. (ii) The meteorites have been exposed to multiple extreme conditions ranging from milliseconds to billions of years duration when traveling through the interplanetary space, until they fell down on an astronomical body like Earth. (iii) Once on Earth, the meteorites get exposed to different weathering conditions, which often makes it a challenge to retrieve their former history in an unambiguous way.

In Colombia, potato crops are affected by a wide variety of viruses such as PVY, PLRV, PVX, PMTV and PVS. Unfortunately, there are very few studies on the biology, distribution and pathogenicity of these viruses; this situation is even worse for the latent virus PVS. In this work, we evaluated the presence of PVS in four Colombian provinces (Antioquia, Boyaca, Cundinamarca, Narino) by the use of ELISA. We also studied the degree of molecular variation by sequence comparison of a segment of the gene encoding for the viral coat protein. In average, PVS was detected in 40% of 320 analyzed samples of potato leaves; the highest levels were observed in the East of Antioquia (49%) and Pasto (Narino) (47%), while in the other regions ranged between 35% and 42%. Analysis of sequence revealed the presence of two PVS strains in Colombia: three isolates were associated to PVSO (Ordinary) and twelve belonged to PVSA (Andean). A high diversity was observed among PVSA strains with percent identities in the range of 88-99%. These findings highlight the importance of strengthening seed certification programs and quarantine measures in Colombia for viruses like PVS, which can cause losses of up to 20% in potato crops and even higher in mixed virus infection.