Mechanism of plant eIF4E-mediated resistance against a Carmovirus (Tombusviridae): cap-independent translation of a viral RNA controlled in cis by an (a)virulence determinant
In this article, Truniger et al. show that a sequence in the 3' untranslated region of the Melon necrotic spot virus (MNSV) genome functions as a cap-independent translational enhancer and that in a viral isolate overcoming eIF4E-mediated resistance in melon this sequence corresponded to the virulence determinant. Based on these findings, they propose a model of the molecular mechanism of this resistance.
The Plant Journal, 16 July 2008, 2008, doi:10.1111/j.1365-313X.2008.03630.x
Chloroplastic protein NRIP1 mediates innate immune receptor recognition of a viral effector
With regard to the plant innate immunity, Caplan and her collaborators describe in this paper the identification and characterization of a chloroplastic protein (NRIP1) that interacts with the N immune receptor, which responsible for the recognition in tobacco of the p50 helicase domain (avr) of Tobacco mosaic virus (TMV), an event that triggers the plant innate immunity. Their data suggest that p50 and NRIP1, possibly along with other host proteins, constitute a prerecognition complex required for N's activation.
Cell, 7 February 2008, 2008, volume 132 (3), pages 449-462, doi:10.1016/j.cell.2007.12.031
Specific targeting of a plasmodesmal protein affecting cell-to-cell communication
Plasmodesmata provide the channels for cell-to-cell communication in plants, contributing, among other functions, to viral translocation. Despite their central role, little is known about how plasmodesmata work. Thomas and collaborators describe in this paper the identification and characterisation of a novel family of plasmodesmata-located proteins called PDLP1. They showed that members of this family affect cell-to-cell communication, identifying a mode of intercellular trafficking and targeting novel for plant biology.
PLoS Biology, 22 January 2008, 2008, volume 6 (1), e7, doi:10.1371/journal.pbio.0060007
Natural variation and functional analyses provide evidence for co-evolution between plant elF4E and potyviral VPg
The co-evolution of plant resistance gene encoding eIF4E and avirulence gene vpg (VPg) is demonstrated in a recent study from Charron and her collaborators by combining genetic diversity and functional analyses. The authors show resistance phenotypes arose from disruption of the interaction between eIF4E and VPg and that the viral adaptation to eIF4E-mediatied resistance resulted from restored interaction with resistance protein.
The Plant Journal, 8 January 2008, 2008, volume 54 (1), pages 56-68, doi:10.1111/j.1365-313X.2008.03407.x
Tobacco Mosaic Virus replicase-auxin/indole acetic acid protein interactions: reprogramming the auxin response pathway to enhance virus infection
Culver and his collaborators have examined in tomato the role of the interaction of the TMV replicase with auxin/indole acetic acid proteins in virus pathogenicity. They used a TMV mutant with a reduced ability to interact with specific auxin/indole acetic acid proteins and have compared young and mature leaf tissues. They suggest that these interactions enhance virus pathogenicity in tissues where auxin/indole acetic acid proteins accumulate and speculate that the virus disrupts Aux/IAA functions as a means to reprogram the cellular environment of older cells to one that is more compatible for virus replication and spread.
Journal of Virology, 19 December 2007, 2008, volume 82 (5), pages 2477-2485, doi:10.1128/JVI.01865-07
Methyl Salicylate is a critical mobile signal for Plant Systemic Acquired resistance
Systemic acquired resistance (SAR), an state of enhanced defence to infections subsequent to a primary one, requires movement trough the phloem of a signal from the primarily infected tissue to the systemic tissue. The nature of this signal has remained elusive. Park and his colleagues, by using an elegant combination of genetic, physiological and biochemical analysis, showed that methyl salycilate is a SAR signal in tobacco.
Science, 5 October 2007, 2007, volume 318 (5847), pages 113-116, doi:10.1126/science.1147113
An inhibitor of viral RNA replication is encoded by a plant resistance gene
Several plant genes conferring dominant resistance to viruses have been cloned and characterised to date. Ishibashi and his collaborators report in this paper the cloning and characterization of Tm-1, a gene that confers semidominant resistance to Tomato mosaic virus (ToMV). Their results indicate that Tm-1 codes for an inhibitor of ToMV replication which is constitutively expressed in cells. Thus, Tm-1 seems to have characteristics different from those of previously identified virus resistance genes in plants.
PNAS, 21 August 2007, 2007, volume 104 (34), 2007, pages 13833-13838, doi:10.1073/pnas.0703203104
Infection and coaccumulation of tobacco mosaic virus proteins alter microRNA levels, correlating with symptom and plant developement
The molecular processes responsible for the development of disease symptoms are still largely unknown. In a publication from Bazzini and collaborators, an account was given on the exploitation or use by plant viruses of the miRNA pathways during pathogenesis. The authors present evidence that virus infection and viral proteins influence miRNA balance without affecting posttranscriptional gene silencing, an effect that may impact disease symptoms in infected plants.
PNAS, 17 July 2007, 2007, volume 104 (29), pages 12157-12162, doi:10.1073/pnas.0705114104
A novel role for the TIR domain in association with pathogen-derived elicitors
Burch-Smith and collaborators provide in this paper a novel insight into how resistance proteins (R) involved in plant innate immunity recognize the presence of pathogen-derived avirulence (avr) proteins. Working with the tobacco N gene (R) and the p50 helicase domain (avr) of Tobacco mosaic virus, they demonstrated for the first time that the recognition mechanism by a R protein involves not only multicellular compartments but also the formation of multiple protein complexes.
PLoS Biology, 13 February 2007, 2007, volume 5 (3), e68, doi:10.1371/journal.pbio.0050068
Expression of artificial microRNAs in transgenic Arabidopsis thaliana confers virus resistance
Qi-Wen Niu and his collaborators have used an artificial microRNAs (amiRNA)-mediated approach to confer virus resistance in transgenic Arabidopsis thaliana. Resistance is displayed at the cell level, is heritable, and is maintained at temperatures that compromise small interfering RNA-mediated resistance. Their study pointed out to the possibility of engineering broad spectrum resistance to several viruses by co-expression of appropriately designed multiple amiRNAs.
Nature Biotechnology, 22 October 2006, 2006, volume 24, pages 1420-1428, doi:10.1038/nbt1255
Peptide Aptamers that binds to a Geminivirus replication protein interferes with viral replication in plant cells
Peptide aptamers, a relatively new technology, can contribute to the functional analysis of pathogen-driven processes but also can provide important tools for pathogen control. Lopez-Ochoa and her colleagues used for the first time this technology to inhibit the replication of a plant DNA virus, supporting the possibility of using aptamer technology to develop broad-based resistance against virus induced-diseases in crops.
Journal of Virology, 18 March 2006, 2006, volume 80 (12), pages 5841-5853, doi:10.1128/JVI.02698-05