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Viral factors involved in plant pathogenesis

Curr Opin Virol. 2015; 11C: 21-30.

García JA, Pallás V.

Curr Opin Virol. 2015; 11C: 21-30Plant viruses must usurp host factors/routes for their survival. Disturbances derived from this extreme dependence for host resources, together with physiological alterations associated with defensive responses, can cause, in some virus–host combinations, acute or chronic plant diseases. As the coding capacity of these biotrophic pathogens is limited, viral-encoded proteins must essentially be multifunctional proteins involved in very different steps of their life cycle, and are usually elicitors of defensive responses. Thus, most, if not all, viral-encoded proteins can act as pathogenicity determinants. Indeed, the viral proteins involved in the essential processes of their life cycle, such as replication, movement, encapsidation and transmission can be critical players of the pathogenesis process through direct or indirect interactions.

This review updates our knowledge on how viral factors affect plant physiology and contribute to the development of symptomatology.

Plant embryogenesis requires AUX/LAX-mediated auxin influx

Development. 2015; pii: dev.115832.

Robert HS, Grunewald W, Sauer M, Cannoot B, Soriano M, Swarup R, Weijers D, Bennett M, Boutilier K, Friml J.

Development. 2015; pii: dev.115832The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of the auxin influx carriers AUX1 and LIKE-AUX1 (LAX) proteins is not well established.

Here, we used chemical and genetic tools on Brassica napus microspore-derived embryos and Arabidopsis thaliana zygotic embryos, and demonstrate that AUX1, LAX1 and LAX2 are required for both shoot and root pole formation, in concert with PIN efflux carriers. Furthermore, we uncovered a positive-feedback loop between MONOPTEROS (ARF5)-dependent auxin signalling and auxin transport. This MONOPTEROS-dependent transcriptional regulation of auxin influx (AUX1, LAX1 and LAX2) and auxin efflux (PIN1 and PIN4) carriers by MONOPTEROS helps to maintain proper auxin transport to the root tip.

These results indicate that auxin-dependent cell specification during embryo development requires balanced auxin transport involving both influx and efflux mechanisms, and that this transport is maintained by a positive transcriptional feedback on auxin signalling.

Interleukin 1- and type I interferon-dependent enhancement of the innate immune profile of a NYVAC-HIV-1 Env-Gag-Pol-Nef vaccine vector with dual deletion of type I and type II interferon-binding proteins

J Virol. 2015; pii: JVI.03061-14.

Delaloye J, Filali-Mouhim A, Cameron MJ, Haddad EK, Harari A, Goulet JP, Gomez CE, Perdiguero B, Esteban M, Pantaleo G, Roger T, Sékaly RP, Calandra T.

J Virol. 2015; pii: JVI.03061-14NYVAC, a highly attenuated, replication-restricted poxvirus, is a safe and immunogenic vaccine vector. Deletion of immune evasion genes encoded by poxviruses is an attractive strategy for improving their immunogenic properties.

Using system biology approaches, we herein describe the enhanced immunological profile of NYVAC vectors expressing the HIV-1 clade C env-gag-pol-nef genes (NYVAC-C) with single or double deletion of genes encoding type I (ΔB19R) or type II (ΔB8R) interferon (IFN)-binding proteins. Transcriptomic analyses of human monocytes infected with NYVAC-C, NYVAC-C-ΔB19R or NYVAC-C-ΔB8RB19R revealed a concerted up-regulation of innate immune pathways (IFN-stimulated genes [ISGs]) of increasing magnitude with NYVAC-C-ΔB19R and NYVAC-C-ΔB8RB19R relative to NYVAC-C. Deletion of B8R and B19R resulted in an enhanced activation of IRF3, IRF7 and STAT1, robust production of type I IFN and of ISGs whose expressions were inhibited by anti-type I IFN antibodies. Interestingly, NYVAC-C -ΔB8RB19R induced the production of much higher levels of pro-inflammatory cytokines (TNF, IL-6 and IL-8) than NYVAC-C or NYVAC-C-ΔB19R as well as a strong inflammasome response (caspase-1 and IL-1β) in infected monocytes. Top network analyses showed that this broad ΔB8RB19R-mediated response was organized around two up-regulated gene expression nodes (TNF and IRF7).

Consistent with these findings, monocytes infected with NYVAC-C-ΔB8RB19R induced a stronger type I IFN-dependent and IL-1-dependent allogenic CD4+-T-cell response than NYVAC-C or NYVAC-C-ΔB19R. Dual deletion of type I and type II IFN immune evasion genes in NYVAC markedly enhanced its immunogenic properties via an increased expression of type I IFNs and IL-1β and make it an attractive candidate HIV vaccine vector.

DisA and c-di-AMP act at the intersection between DNA-damage response and stress homeostasis in exponentially growing Bacillus subtilis cells

DNA Repair. 2015; 27C: 1-8.

Gándara C, Alonso JC.

DNA Repair. 2015; 27C: 1-8Bacillus subtilis contains two vegetative diadenylate cyclases, DisA and CdaA, which produce cyclic di-AMP (c-di-AMP), and one phosphodiesterase, GdpP, that degrades it into a linear di-AMP. We report here that DisA and CdaA contribute to elicit repair of DNA damage generated by alkyl groups and H2O2, respectively, during vegetative growth.

disA forms an operon with radA (also termed sms) that encodes a protein distantly related to RecA. Among different DNA damage agents tested, only methyl methane sulfonate (MMS) affected disA null strain viability, while radA showed sensitivity to all of them. A strain lacking both disA and radA was as sensitive to MMS as the most sensitive single parent (epistasis). Low c-di-AMP levels (e.g. by over-expressing GdpP) decreased the ability of cells to repair DNA damage caused by MMS and in less extent by H2O2, while high levels of c-di-AMP (absence of GdpP or expression of sporulation-specific diadenylate cyclase, CdaS) increased cell survival.

Taken together, our results support the idea that c-di-AMP is a crucial signalling molecule involved in DNA repair with DisA and CdaA contributing to modulate different DNA damage responses during exponential growth.

SARS coronaviruses with mutations in E protein are attenuated and promising vaccine candidates

J Virol. 2015; pii: JVI.03566-14.

Regla-Nava JA, Nieto-Torres JL, Jimenez-Guardeño JM, Fernandez-Delgado R, Fett C, Castaño-Rodríguez C, Perlman S, Enjuanes L, DeDiego ML.

J Virol. 2015; pii: JVI.03566-14Severe acute respiratory syndrome coronavirus (SARS-CoV) causes a respiratory disease with a mortality rate of 10%. A mouse-adapted SARS-CoV (SARS-CoV-MA15) lacking the envelope (E) protein (rSARS-CoV-MA15-ΔE) is attenuated in vivo.

To identify E protein regions and host responses that contribute to rSARS-CoV-MA15-ΔE attenuation, several mutants (rSARS-CoV-MA15-E*) containing point mutations or deletions in the amino-terminal or the carboxy-terminal regions of the E protein were generated. Amino acid substitutions in the amino terminus, or deletion of regions in the internal carboxy terminal region of E protein led to virus attenuation. Attenuated viruses induced minimal lung injury, diminished limited neutrophil influx and increased CD4+ and CD8+ T cell counts in the lungs of BALB/c mice, when compared to mice infected with wild type virus. To analyze the host responses leading to rSARS-CoV-MA15-E* attenuation, differences in gene expression elicited by the native and mutant viruses in the lungs of infected mice were determined. Expression levels of a large number of proinflammatory cytokines associated with lung injury were reduced in the lungs of rSARS-CoV-MA15-E* infected mice, whereas the levels of anti-inflammatory cytokines were increased, both at the mRNA and protein levels.

These results suggested that the reduction in lung inflammation together with a more robust antiviral T cell response contributed to rSARS-CoV-MA15-E* attenuation. The attenuated viruses completely protected mice against challenge with the lethal parental virus, indicating that these viruses are promising vaccine candidates.