Highly pathogenic avian influenza A/H5N1 virus can cause morbidity and mortality in humans but thus far has not acquired the ability to be transmitted by aerosol or respiratory droplet ("airborne transmission") between humans. To address the concern that the virus could acquire this ability under natural conditions, we genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets. None of the recipient ferrets died after airborne infection with the mutant A/H5N1 viruses. Four amino acid substitutions in the host receptor-binding protein hemagglutinin, and one in the polymerase complex protein basic polymerase 2, were consistently present in airborne-transmitted viruses. The transmissible viruses were sensitive to the antiviral drug oseltamivir and reacted well with antisera raised against H5 influenza vaccine strains. Thus, avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and therefore constitute a risk for human pandemic influenza.

Airborne transmission of influenza A/H5N1 virus between ferrets

Publisher Summary Cucumber mosaic virus (CMV), the type member of the cucumovirus group, was first reported in 1916 as the causal agent of a disease of cucumber and muskmelon in Michigan and cucumber in New York. Since then, CMV has been found in most countries of the world, predominantly in the temperate zones, but increasingly more often in the tropical countries. CMV has the largest host range of any virus. The number of plant species identified as hosts for CMV has increased steadily over the past 60 years. The highlights of the more recent research include the following: (1) the complete nucleotide sequence of the genome of three strains of CMV has been determined, as well as nucleotide sequences of individual RNAs of eight other CMV strains, (2) the CMV replicase has been purified to homogeneity, and it functions in vitro to synthesize CMV RNA de novo , (3) infectious transcripts have been synthesized from full-length cDNA clones of the three strains of CMV, (4) these biologically active cDNAs are being used to map sequences involved in replication, movement, pathogenesis, resistance, and vector transmission. Biologically active cDNA clones of the satellite RNAs of CMV have been produced in seven laboratories and sequences involved in replication and pathogenicity have/are being identified, (5) finally, transgenic plants have been produced expressing either the CMV coat protein gene or satellite RNA sequences that show to protect such plants from infection by CMV. This chapter, while focusing on the more recent developments in CMV biology and biochemistry, also covers some of the same ground albeit in brief. The chapter presents a comprehensive review that can be used as a reference work for general virologists and plant pathologists, as well as those specializing in the molecular biology of CMV and/or other multicomponent plant viruses.

Cucumber Mosaic Virus

The majority of described plant viruses are transmitted by insects of the Hemipteroid assemblage that includes aphids, whiteflies, leafhoppers, planthoppers, and thrips. In this review we highlight progress made in research on vector interactions of the more than 200 plant viruses that are transmitted by hemipteroid insects beginning a few hours or days after acquisition and for up to the life of the insect, i.e., in a persistentcirculative or persistent-propagative mode. These plant viruses move through the insect vector, from the gut lumen into the hemolymph or other tissues and finally into the salivary glands, from which these viruses are introduced back into the plant host during insect feeding. The movement and/or replication of the viruses in the insect vectors require specific interactions between virus and vector components. Recent investigations have resulted in a better understanding of the replication sites and tissue tropism of several plant viruses that propagate in insect vectors. Furthermore, virus and insect proteins involved in overcoming transmission barriers in the vector have been identified for some virus-vector combinations.

Insect Vector Interactions with Persistently Transmitted Viruses

Plasmodesmata are intercellular organelles in plants that establish cytoplasmic continuity between neighboring cells. Microinjection studies showed that plasmodesmata facilitate the cell-to-cell transport of a plant-encoded transcription factor, KNOTTED1 (KN1). KN1 can also mediate the selective plasmodesmal trafficking of kn1 sense RNA. The emerging picture of plant development suggests that cell fate is determined at least in part by supracellular controls responding to cellular position as well as lineage. One of the mechanisms that enables the necessary intercellular communication appears to involve transfer of informational molecules (proteins and RNA) through plasmodesmata.

https://science.sciencemag.org/content/sci/270/5244/1980.full.pdf

Selective Trafficking of KNOTTED1 Homeodomain Protein and Its mRNA Through Plasmodesmata

While evolution by natural selection has long been a foundation for biomedical science, it has recently gained new power to explain many aspects of disease. This progress results largely from the disciplined application of what has been called the adaptations program. We show that this increasingly significant research paradigm can predict otherwise unsuspected facets of human biology, and that it provides new insights into the causes of medical disorders, such as those discussed below: 1. Infection. Signs and symptoms of the host-parasite contest can be categorized according to whether they represent adaptations or costs for host or parasite. Some host adaptations may have contributed to fitness in the Stone Age but are obsolete today. Others, such as fever and iron sequestration, have been incorrectly considered harmful. Pathogens, with their large populations and many generations in a single host, can evolve very rapidly. Acquisition of resistance to antibiotics is one example. Another is the recently demonstrated tendency to change virulence levels in predictable ways in response to changed conditions imposed incidentally by human activities. 2. Injuries and toxins. Mechanical injuries or stressful wear and tear are conceptually simpler than infectious diseases because they are not contests between conflicting interests. Plant-herbivore contests may often underlie chemical injury from the defensive secondary compounds of plant tissues. Nausea in pregnancy, and allergy, may be adaptations against such toxins. 3. Genetic factors. Common genetic diseases often result from genes maintained by other beneficial effects in historically normal environments. The diseases of aging are especially likely to be associated with early benefits. 4. Abnormal environments. Human biology is designed for Stone Age conditions. Modern environments may cause many diseases-for example, deficiency syndromes such as scurvy and rickets, the effects of excess consumption of normally scarce nutrients such as fat and salt, developmental diseases such as myopia, and psychological reactions to novel environments. The substantial benefits of evolutionary studies of disease will be realized only if they become central to medical curricula, an advance that may at first require the establishment of one or more research centers dedicated to the further development of Darwinian medicine.

/pdf/the-dawn-of-darwinian-medicine-3owvw6gtge.pdf

The Dawn of Darwinian Medicine

The function of the 30-kilodalton movement protein (MP) of tobacco mosaic virus is to facilitate cell-to-cell movement of viral progeny in an infected plant. A novel method for delivering non-plasmalemma-permeable fluorescent probes to the cytosol of spongy mesophyll cells of tobacco leaves was used to study plasmodesmatal size exclusion limits in transgenic plants that express the MP gene. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran) with an average molecular mass of 9400 daltons and an approximate Stokes radius of 2.4 nanometers was detected between cells of the transgenic plants, whereas the size exclusion limit for the control plants was 700 to 800 daltons. No evidence of F-dextran metabolism in the leaves of the transgenic plants was found. Thus, the tobacco mosaic virus movement protein has a direct effect on a plasmodesmatal function.

https://science.sciencemag.org/content/sci/246/4928/377.full.pdf

Movement Protein of Tobacco Mosaic Virus Modifies Plasmodesmatal Size Exclusion Limit

The proposed role of the 30-kilodalton(kD) protein of tobacco mosaic virus is to facilitate cell-to-cell spread of the virus-during infection. To directly define the function of the protein, a chimeric gene containing a cloned complementary DNA of the 30-kD protein gene was introduced into tobacco cells via a Ti plasmid-mediated transformation system of Agrobacterium tumefaciens. Transgenic plants regenerated from transformed tobacco cells expressed the 30-kD protein messenger RNA and accumulated 30-kD protein. Seedlings expressing the 30-kD protein gene complemented the Lsl mutant of TMV, a mutant that is temperature-sensitive in cell-to-cell movement. In addition, enhanced movement of the Lsl virus at the permissive temperature was detected in seedlings that express the 30-kD protein gene. These results conclusively demonstrate that the 30-kD protein of tobacco mosaic virus potentiates the movement of the virus from cell to cell.

https://science.sciencemag.org/content/sci/237/4813/389.full.pdf

The 30-kilodalton gene product of tobacco mosaic virus potentiates virus movement.

We previously demonstrated, in transgenic tobacco plants, that the role of the movement protein (MP) of tobacco mosaic virus is to facilitate the cell-to-cell spread of viral progeny during infection. An analysis of different tissues of these transgenic plants indicated that the MP accumulated in leaf, stem, and root tissue. The highest levels were detected in older leaves. The relative levels of MP in leaf tissue from transgenic plants were equivalent to, or higher than, the levels of MP in tobacco mosaic virus-infected leaf tissue. Results of subcellular fractionation of homogenates of transgenic leaf tissue showed that the MP was most abundant in the cell wall fraction of older leaves and that the protein remained at high levels in the cell wall fraction as the leaves continued to age. Significant levels of the MP were detected in a crude membrane/organelle fraction and a soluble fraction in younger leaves but decreased to low levels in older leaves. These results suggest that the MP accumulates and is stable in cell walls. We have previously shown that the MP modifies the molecular exclusion limit of plasmodesmata, which is consistent with the hypothesis that plant viruses move from cell to cell through altered plasmodesmata. We show here that the ability of the tobacco mosaic virus MP to modify the molecular exclusion limit of plasmodesmata in tobacco depends on the developmental stage of the leaf. The implications of these findings on understanding virus movement and how plasmodesmata function are discussed.

/pdf/molecular-characterization-and-biological-function-of-the-3hr47ezo00.pdf

Molecular characterization and biological function of the movement protein of tobacco mosaic virus in transgenic plants.

A gene encoding a temperature-sensitive mutant (MPP154A) of the 30-kilodalton movement protein (MP) of tobacco mosaic virus (TMV) was transformed into Nicotiana tabacum cv Xanthi. Transgenic plants expressing the MPP154A gene complemented local and systemic movement of an MP-defective mutant of TMV (U3/12MPfs) at the permissive temperature of 24 degrees C but not at 32 degrees C, the nonpermissive temperature. A microinjection procedure was used to investigate the effects of the modified TMV MP on plasmodesmatal size-exclusion limits. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran), with an average molecular mass of 9.4 kilodaltons, was detected between leaf mesophyll cells of the transgenic plants at 24 degrees C; however, no movement of either 3.9-kilodalton or 9.4-kilodalton F-dextrans was detected when the transgenic plants were held for 6 hours (or longer) at 32 degrees C. When these plants were shifted back to 24 degrees C for 6 hours, cell-to-cell movement of the F-dextrans was again observed. Accumulation of MPP154A was not affected by the temperature regime, nor was the subcellular distribution of the MP altered. These results are consistent with a change in the protein conformation of MPP154A at the nonpermissive temperature, which gives rise to a protein that fails to modify the molecular size-exclusion limits of plasmodesmata to the same extent as wild-type MP. Surprisingly, at 32 degrees C, movement of the F-dextrans was inhibited in transgenic plants expressing the wild-type MP gene; however, the inhibition was transient and was no longer detected after 48 hours at this elevated temperature. This transient inhibition of plasmodesmatal function was alleviated with Sirofluor, an inhibitor of callose ([1----3]-beta-D-glucan) synthesis. This result provides experimental evidence that callose deposition is involved in regulating the molecular size-exclusion limit of plasmodesmata in plants. Sirofluor had no effect on the inhibition of F-dextran movement at 32 degrees C in plants expressing the MPP154A gene, indicating that callose formation was not responsible for the failure of the temperature-sensitive mutant protein to alter the size-exclusion limit of plasmodesmata.

Plasmodesmatal function is probed using transgenic tobacco plants that express a virus movement protein.

The Groundnut Department at National Semi-Arid Research Resources Institute (NaSARRI) is mandated to conduct research on groundnuts ( Arachis hypogaea L) in Uganda. It undertakes research aimed at cultivar development, maintenance and conservation through germplasm collection, characterization, evaluation, breeding, maintenance and generation of appropriate crop management technologies for sustained production. Most of the varieties traditionally grown by farmers in Uganda are landraces adapted more for survival than yield. Yields from such varieties average 800 kg/ha of dry pods yet yields of 3,000kg/ha have been achieved from on-station plots. Yields per hectare are low, because of a combination of factors such as unreliable rains, mostly non-irrigated cultures, traditional small-scale farming with little mechanization, outbreaks of pest infestations and diseases, the use of low-yielding seed varieties and increased and/or continued cultivation on marginal land. Political instability and the frequently unsupportive oilseed policies have also played their role in low groundnut productivity. Therefore, there is excellent potential for yield improvement. Research efforts have, since the 1920s, endeavored to breed varieties that are high yielding, resistant to major pests and diseases, tolerant to drought, high in oil content and have a short to medium maturity period, as well as to develop appropriate production packages. These efforts have resulted in the release of 14 varieties, the most recent being Igola-1, Serenut 1R, Serenut 2T, Serenut 3R and Serenut 4T. These varieties have helped to alleviate some of the production problems listed above. However, the market and field stability of those varieties, in light of emerging stresses, calls for continuous research while at the same time keeping crop improvement, quality and safety linked to practical applications. Emerging issues like aflatoxin, leafminers and biotechnology need to be addressed and incorporated into the research agenda. Deployment of novel breeding approaches like molecular breeding to complement conventional breeding would increase the efficiency of cultivar development. Additionally, to maintain or increase market share, producers and exporters need to adapt the type of groundnuts being cultivated to consumer requirements. Key words: Arachis, Breeding NaSARRI, Uganda,

/pdf/overview-of-groundnuts-research-in-uganda-past-present-and-55ry4pq2n5.pdf

Carl M. Deom

Papers

Movement Protein of Tobacco Mosaic Virus Modifies Plasmodesmatal Size Exclusion Limit

The 30-kilodalton gene product of tobacco mosaic virus potentiates virus movement.

Molecular characterization and biological function of the movement protein of tobacco mosaic virus in transgenic plants.

Plasmodesmatal function is probed using transgenic tobacco plants that express a virus movement protein.

Overview of groundnuts research in Uganda: Past, present and future