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
Article first published online: 15 AUG 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
The Plant Journal
Volume 56, Issue 5, pages 716–727, December 2008
How to Cite
Truniger, V., Nieto, C., González-Ibeas, D. and Aranda, M. (2008), 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. The Plant Journal, 56: 716–727. doi: 10.1111/j.1365-313X.2008.03630.x
- Issue published online: 27 NOV 2008
- Article first published online: 15 AUG 2008
- Received 14 May 2008; revised 26 June 2008; accepted 1 July 2008; published online 15 August 2008.
- cap-independent translation;
- Melon necrotic spot virus;
- recessive resistance;
- resistance breaking
Translation initiation factors are universal determinants of plant susceptibility to RNA viruses, but the underlying mechanisms are poorly understood. Here, we show that a sequence in the 3′ untranslated region (3′-UTR) of a viral genome that is responsible for overcoming plant eIF4E-mediated resistance (virulence determinant) functions as a 3′ cap-independent translational enhancer (3′-CITE). The virus/plant pair studied here is Melon necrotic spot virus (MNSV) and melon, for which a recessive resistance controlled by melon eIF4E was previously described. Chimeric viruses between virulent and avirulent isolates enabled us to map the virulence and avirulence determinants to 49 and 26 nucleotides, respectively. The translational efficiency of a luc reporter gene flanked by 5′- and 3′-UTRs from virulent, avirulent and chimeric viruses was analysed in vitro, in wheatgerm extract, and in vivo, in melon protoplasts, showing that: (i) the virulence determinant mediates the efficient cap-independent translation in vitro and in vivo; (ii) the avirulence determinant was able to promote efficient cap-independent translation in vitro, but only when eIF4E from susceptible melon was added in trans, and, coherently, only in protoplasts of susceptible melon, but not in the protoplasts of resistant melon; (iii) these activities required the 5′-UTR of MNSV in cis. Thus, the virulence and avirulence determinants function as 3′-CITEs. The activity of these 3′-CITEs was host specific, suggesting that an inefficient interaction between the viral 3′-CITE of the avirulent isolate and eIF4E of resistant melon impedes the correct formation of the translation initiation complex at the viral RNA ends, thereby leading to resistance.