Nonstructural protein 14 (nsp14) of coronaviruses (CoV) is important for viral replication and transcription. The N-terminal exoribonuclease (ExoN) domain plays a proofreading role for prevention of lethal mutagenesis, and the C-terminal domain functions as a (guanine-N7) methyl transferase (N7-MTase) for mRNA capping. The molecular basis of both these functions is unknown. Here, we describe crystal structures of severe acute respiratory syndrome (SARS)-CoV nsp14 in complex with its activator nonstructural protein10 (nsp10) and functional ligands. One molecule of nsp10 interacts with ExoN of nsp14 to stabilize it and stimulate its activity. Although the catalytic core of nsp14 ExoN is reminiscent of proofreading exonucleases, the presence of two zinc fingers sets it apart from homologs. Mutagenesis studies indicate that both these zinc fingers are essential for the function of nsp14. We show that a DEEDh (the five catalytic amino acids) motif drives nucleotide excision. The N7-MTase domain exhibits a noncanonical MTase fold with a rare β-sheet insertion and a peripheral zinc finger. The cap-precursor guanosine-P3-adenosine-5′,5′-triphosphate and S-adenosyl methionine bind in proximity in a highly constricted pocket between two β-sheets to accomplish methyl transfer. Our studies provide the first glimpses, to our knowledge, into the architecture of the nsp14-nsp10 complex involved in RNA viral proofreading.CoV | nsp14 | proofreading | exoribonuclease | methyltransferase

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Plant reoviruses are thought to replicate and assemble within cytoplasmic, nonmembranous structures called viroplasms. Here, we established continuous cell cultures of the white-backed planthopper (Sogatella furcifera Horváth) to investigate the mechanisms for the genesis and maturation of the viroplasm induced by Southern rice black-streaked dwarf virus (SRBSDV), a fijivirus in the family Reoviridae, during infection of its insect vector. Electron and confocal microscopy revealed that the viroplasm consisted of a granular region, where viral RNAs and nonstructural proteins P6 and P9-1 accumulated, and a filamentous region, where viral RNAs, progeny cores, viral particles, as well as nonstructural proteins P5 and P6 accumulated. Our results suggested that the filamentous viroplasm matrix was the site for the assembly of progeny virions. Because viral RNAs were produced by assembled core particles within the filamentous viroplasm matrix, we propose that these viral RNAs might be transported to the granular viroplasm matrix. P5 formed filamentous inclusions and P9-1 formed granular inclusions in the absence of viral infection, suggesting that the filamentous and granular viroplasm matrices were formed primarily by P5 and P9-1, respectively. P6 was apparently recruited in the whole viroplasm matrix by direct interaction with P9-1 and P5. Thus, the present results suggested that P5, P6, and P9-1 are collectively required for the genesis and maturation of the filamentous and granular viroplasm matrix induced by SRBSDV infection. Based on these results, we propose a new model to explain the genesis and maturation of the viroplasms induced by fijiviruses in insect vector cells.

Successful adaptation of a plant species is dependent upon the programming of critical growth stages so that the plant can capitalize on favorable weather periods during the growing season (Dominique and Andrew, 2010). Plants have evolved a variety of adaptive mechanisms that allow them to optimize growth and development while coping with environmental stresses. These mechanisms include seed and bud dormancy, photoperiod sensitivity, and low-temperature response and others (Fowler et al., 1999;Caius, 2010;Clint and Malcolm, 2007). Seed dormancy delays germination until after the embryo has gone through an after-ripening period. The overwinter survival of buds of many temperate zone trees and shrubs is dependent on a dormancy stage that starts in the late summer or early fall and ends after exposure to an extended period of cold or increasing day length in the spring. In addition to trees, many other dicots and grasses have a photoperiod response that can advance or delay flowering. Vernalization is a requirement for growth at low temperatures before a plant will flower. Most winter annual and biennial plants have a vernalization requirement. Low-temperature acclimation is an ability of plants to cold acclimate when exposed to gradually decreasing temperatures below a specific threshold. This is the most common mechanism that plants have evolved for adapting to low-temperature stress and examples of plants with the capacity to cold harden can be found in most species (Fowler et al., 1999;Nilson and Assmann, 2007;von Caemmerer and Baker, 2007;David and Jacqueline, 2010 AbstractIn the past few years, the signal transduction of the plant hormone abscisic acid (ABA) has been studied extensively and has revealed an unanticipated complex. ABA, characterized as an intracellular messenger, has been proven to act a critical function at the heart of a signaling network operation. It has been found that ABA plays an important role in improving plant tolerance to cold, as well as triggering leaf senescence for years. In addition, there have been many reports suggesting that the signaling pathways for leaf senescence and plant defense responses may overlap. Therefore, the objective was to review what is known about the involvement of ABA signaling in plant responses to cold stress and regulation of leaf senescence. An overview about how ABA is integrated into sugars and reactive oxygen species signaling pathways, to regulate plant cold tolerance and leaf senescence, is provided. These roles can provide important implications for biotechnologically improving plant cold tolerance.

Forsythoside A is a polyphenolic constituent of the fruits of Forsythia suspensa Vahl. which is widely used as an antiinflammatory agent in traditional Chinese medicine. In the present study, the effects of forsythoside A on cell infection by avian infectious bronchitis virus were assessed. A real-time fluorescence quantitative PCR assay was used to determine mRNA content of IBV N gene. The pretreatment of cells with forsythoside A, adding forsythoside A post infection of cells, and treatment of virus with forsythoside A were analysed. The inhibitory effect of forsythoside A was confirmed by infecting primary chicken embryo kidney cells. Infected cells were inhibited by forsythoside A treatment. The data indicated that forsythoside A has the potential to prevent IBV infection in vitro. Copyright © 2010 John Wiley & Sons, Ltd.