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Identification of the domains of cauliflower mosaic virus protein P6 responsible for suppression of RNA silencing and salicylic acid signalling.

Authors
  • Laird, Janet1
  • McInally, Carol
  • Carr, Craig
  • Doddiah, Sowjanya
  • Yates, Gary
  • Chrysanthou, Elina
  • Khattab, Ahmed
  • Love, Andrew J
  • Geri, Chiara
  • Sadanandom, Ari
  • Smith, Brian O
  • Kobayashi, Kappei
  • Milner, Joel J
  • 1 Plant Science Research Theme, School of Life Sciences and Institute of Molecular Cellular and Systems Biology, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
Type
Published Article
Journal
Journal of General Virology
Publisher
Microbiology Society
Publication Date
December 2013
Volume
94
Issue
Pt 12
Pages
2777–2789
Identifiers
DOI: 10.1099/vir.0.057729-0
PMID: 24088344
Source
Medline
License
Unknown

Abstract

Cauliflower mosaic virus (CaMV) encodes a 520 aa polypeptide, P6, which participates in several essential activities in the virus life cycle including suppressing RNA silencing and salicylic acid-responsive defence signalling. We infected Arabidopsis with CaMV mutants containing short in-frame deletions within the P6 ORF. A deletion in the distal end of domain D-I (the N-terminal 112 aa) of P6 did not affect virus replication but compromised symptom development and curtailed the ability to restore GFP fluorescence in a GFP-silenced transgenic Arabidopsis line. A deletion in the minimum transactivator domain was defective in virus replication but retained the capacity to suppress RNA silencing locally. Symptom expression in CaMV-infected plants is apparently linked to the ability to suppress RNA silencing. When transiently co-expressed with tomato bushy stunt virus P19, an elicitor of programmed cell death in Nicotiana tabacum, WT P6 suppressed the hypersensitive response, but three mutants, two with deletions within the distal end of domain D-I and one involving the N-terminal nuclear export signal (NES), were unable to do so. Deleting the N-terminal 20 aa also abolished the suppression of pathogen-associated molecular pattern-dependent PR1a expression following agroinfiltration. However, the two other deletions in domain D-I retained this activity, evidence that the mechanisms underlying these functions are not identical. The D-I domain of P6 when expressed alone failed to suppress either cell death or PR1a expression and is therefore necessary but not sufficient for all three defence suppression activities. Consequently, concerns about the biosafety of genetically modified crops carrying truncated ORFVI sequences appear unfounded.

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