Biomedical subjects

Fernando García-Arenal

Publications and source records attributed to Fernando García-Arenal.

9 recordsLinked to original sources

PubMed2006

Association and host selectivity in multi-host pathogens.

The distribution of multi-host pathogens over their host range conditions their population dynamics and structure. Also, host co-infection by different pathogens may have important consequences for the evolution of hosts and pathogens, and host-pathogen co-evolution. Hence it is of interest to know if the distribution of pathogens over their host range is random, or if there are associations between hosts and pathogens, or between pathogens sharing a host. To analyse these issues we propose indices for the observed patterns of host infection by pathogens, and for the observed patterns of co-infection, and tests to analyse if these patterns conform to randomness or reflect associations. Applying these tests to the prevalence of five plant viruses on 21 wild plant species evidenced host-virus associations: most hosts and viruses were selective for viruses and hosts, respectively. Interestingly, the more host-selective viruses were the more prevalent ones, suggesting that host specialisation is a successful strategy for multi-host pathogens. Analyses also showed that viruses tended to associate positively in co-infected hosts. The developed indices and tests provide the tools to analyse how strong and common are these associations among different groups of pathogens, which will help to understand and model the population biology of multi-host pathogens.

Ecosystem↗

PubMed2006

Comparison of properties of particles of Cucumber mosaic virus and Tomato aspermy virus based on the analysis of molecular surfaces of capsids.

The plant RNA viruses Cucumber mosaic virus (CMV) and Tomato aspermy virus (TAV) (genus Cucumovirus) have similar icosahedral particles, the crystal structures of which have been reported recently. Similarity in particle structure agrees with reports of stable capsids assembled from their capsid proteins and of viable recombinant viruses with chimeric capsid proteins derived from CMV and TAV. However, differences between the cucumoviruses have been reported for physicochemical properties. Here, structural and electrostatic features of the molecular surfaces are studied to investigate their relationship with these observations. Two coat-protein recombinants with structures modelled by taking CMV and TAV as templates were also included in the analysis. Results show that there exists an external region of negative electrostatic potential that has arisen from strictly conserved charged residues situated near the external HI loop of the subunits in the capsomers. This negative domain surrounds the fivefold and quasi-sixfold axes and locates above regions of positive potential that extend to cover, nearly homogeneously, the inner surface of capsids, where interaction with encapsidated RNA occurs. Differences between the outer electrostatic distributions in CMV and TAV explain the distinct response of both viruses to variations in physicochemical conditions required for particle stability and are essential to rationalize the biological activity of the coat-protein recombinants, in spite of their seemingly distinct electrostatic characteristics.

Capsid↗

PubMed2006

Analysis of the viability of coat-protein hybrids between Cucumber mosaic virus and Tomato aspermy virus.

Coat-protein (CP) hybrids between Cucumber mosaic virus (CMV) and Tomato aspermy virus (TAV) were engineered to analyse reported CP-associated differences between these viruses. CP portions delimited by aa 1-59, 60-148 and 149-219 were exchanged in all possible combinations within TAV RNA3. The seven possible chimeras were able to replicate in tobacco protoplasts to similar levels, but only those having residues 1-59 or 60-148 from CMV were infectious to tobacco plants, a common host for CMV and TAV, and formed stable particles. When most of the movement protein (MP) of TAV was substituted for that of CMV, infectivity of CP hybrids did not vary. No hybrid was able to infect cucumber plants, a host for CMV and not for TAV. Need for MP-CP compatibility could explain these results, but shows that MP-CP compatibility conditions the use of CP chimeras to map CP-associated differences between CMV and TAV.

Capsid Proteins↗

PubMed2005

Role of recombination in the evolution of natural populations of Cucumber mosaic virus, a tripartite RNA plant virus.

The role of recombination in the evolution of Cucumber mosaic virus (CMV) was analyzed in a collection of Spanish isolates from 1989 to 2002. Isolates were characterized by ribonuclease protection assay using six RNA probes, two for each of the three genomic RNAs, which allowed the identification of the analyzed regions as belonging to CMV isolates in subgroups IA, IB, and II. Most isolates belonged to subgroups IA (64%) and IB (12%), 5% were reassortants among subgroups IA, IB, or II, and 17% were recombinants between these groups. Recombinants at RNA3 were significantly more frequent than recombinants at RNAs 1 and 2. One IB-IA recombinant RNA3 was as frequent in central Spain as the IA RNA3. The genetic structure of the virus population suggested that reassortants and most recombinant genotypes were selected against and was consistent with a higher biological cost of reassortment than recombination. Data also suggest that recombinants that encode hybrid proteins are at a higher disadvantage than recombinants that exchange whole ORFs.

Cucumovirus↗

PubMed2003

Variation and evolution of plant virus populations.

Over the last 15 years, interest in plant virus evolution has re-emerged, as shown by the increasing number of papers published on this subject. In recent times, research in plant virus evolution has been viewed from a molecular, rather than populational, standpoint, and there is a need for work aimed at understanding the processes involved in plant virus evolution. However, accumulated data from analyses of experimental and natural populations of plant viruses are beginning to delineate some trends that often run contrary to accepted opinion: (1) high mutation rates are not necessarily adaptive, as a large fraction of the mutations are deleterious or lethal; (2) in spite of high potential for genetic variation, populations of plant viruses are not highly variable, and genetic stability is the rule rather than the exception; (3) the degree of constriction of genetic variation in virus-encoded proteins is similar to that in their eukaryotic hosts and vectors; and (4) in spite of huge census sizes of plant virus populations, selection is not the sole factor that shapes their evolution, and genetic drift may be important. Here, we review recent advances in understanding plant virus evolution, and describe the experimental and analytical methods most suited to this purpose.

Biological Evolution↗

PubMed2003

Cucumoviruses.

Research on the molecular biology of cucumoviruses and their plant-virus interactions has been very extensive in the last decade. Cucumovirus genome structures have been analyzed, giving new insights into their genetic variability, evolution, and taxonomy. A new viral gene has been discovered, and its role in promoting virus infection has been delineated. The localization and various functions of each viral-encoded gene product have been established. The particle structures of Cucumber mosaic virus (CMV) and Tomato aspermy virus have been determined. Pathogenicity domains have been mapped, and barriers to virus infection have been localized. The movement pathways of the viruses in some hosts have been discerned, and viral mutants affecting the movement processes have been identified. Host responses to viral infection have been characterized, both temporally and spatially. Progress has been made in determining the mechanisms of replication, gene expression, and transmission of CMV. The pathogenicity determinants of various satellite RNAs have been characterized, and the importance of secondary structure in satellite RNA-mediated interactions has been recognized. Novel plant genes specifying resistance to infection by CMV have been identified. In some cases, these genes have been mapped, and one resistance gene to CMV has been isolated and characterized. Pathogen-derived resistance has been demonstrated against CMV using various segments of the CMV genome, and the mechanisms of some of these forms of resistances have been analyzed. Finally, the nature of synergistic interactions between CMV and other viruses has been characterized. This review highlights these various achievements in the context of the previous work on the biology of cucumoviruses and their interactions with plants.

Biological Evolution↗

PubMed2003

The evolution of virulence in a plant virus.

The evolution of virulence is a rapidly growing field of research, but few reports deal with the evolution of virulence in natural populations of parasites. We present here an observational and experimental analysis of the evolution of virulence of the plant virus Cucumber mosaic virus (CMV) during an epidemic on tomato in eastern Spain. Three types of CMV isolates were found that caused in tomato plants either a systemic necrosis (N isolates), stunting and a severe reduction of leaf lamina (Y isolates), or stunting and leaf curl (A isolates). These phenotypes were due to the presence of satellite RNAs (satRNAs) necrogenic (in N isolates) or attenuative (in A isolates) of the symptoms caused by CMV without satRNA (Y isolates). For these three types of isolates, parameters of virulence and transmission were estimated experimentally. For virulence the ranking of isolates was N > Y > A, for transmissibility, Y > A > N. The predictions of theoretical models for the evolution of virulence were analyzed with these parameters and compared with observations from the field. A single-infection model predicted adequately the observed long-term evolution of the CMV population to intermediate levels of virulence. A coinfection model that considered competition between isolates with an effect on transmission explained the invasion of the CMV population by N isolates at the beginning of the epidemic, and its predictions also agreed with field data on the long-term evolution of the CMV population. An important conclusion from both models was that the density of the aphid vector's population is a major factor in the evolution of CMV virulence. This may be relevant for the design of control strategies for CMV-induced diseases.

Biological Evolution↗

PubMed2003

Estimation of population bottlenecks during systemic movement of tobacco mosaic virus in tobacco plants.

More often than not, analyses of virus evolution have considered that virus populations are so large that evolution can be explained by purely deterministic models. However, virus populations could have much smaller effective numbers than the huge reported census numbers, and random genetic drift could be important in virus evolution. A reason for this would be population bottlenecks during the virus life cycle. Here we report a quantitative estimate of population bottlenecks during the systemic colonization of tobacco leaves by Tobacco mosaic virus (TMV). Our analysis is based on the experimental estimation of the frequency of different genotypes of TMV in the inoculated leaf, and in systemically infected leaves, of tobacco plants coinoculated with two TMV genotypes. A simple model, based on the probability that a leaf in coinoculated plants is infected by just one genotype and on the frequency of each genotype in the source, was used to estimate the effective number of founders for the populations in each leaf. Results from the analysis of three leaves per plant in plants inoculated with different combinations of three TMV genotypes yielded highly consistent estimates. Founder numbers for each leaf were small, in the order of units. This would result in effective population numbers much smaller than the census numbers and indicates that random effects due to genetic drift should be considered for understanding virus evolution within an infected plant.

Genotype↗

PubMed2002

The rate and character of spontaneous mutation in an RNA virus.

Estimates of spontaneous mutation rates for RNA viruses are few and uncertain, most notably due to their dependence on tiny mutation reporter sequences that may not well represent the whole genome. We report here an estimate of the spontaneous mutation rate of tobacco mosaic virus using an 804-base cognate mutational target, the viral MP gene that encodes the movement protein (MP). Selection against newly arising mutants was countered by providing MP function from a transgene. The estimated genomic mutation rate was on the lower side of the range previously estimated for lytic animal riboviruses. We also present the first unbiased riboviral mutational spectrum. The proportion of base substitutions is the same as that in a retrovirus but is lower than that in most DNA-based organisms. Although the MP mutant frequency was 0.02-0.05, 35% of the sequenced mutants contained two or more mutations. Therefore, the mutation process in populations of TMV and perhaps of riboviruses generally differs profoundly from that in populations of DNA-based microbes and may be strongly influenced by a subpopulation of mutator polymerases.

Base Sequence↗