A coiled-coil interaction mediates cauliflower mosaic virus cell-to-cell movement

doi:10.1073/pnas.0407731102

A coiled-coil interaction mediates cauliflower mosaic virus cell-to-cell movement

^∥Friedrich Miescher Institute, P.O. Box 2543, CH-4002, Basel, Switzerland; ^*Istituto di Virologia Vegetale, Consiglio Nazionale delle Ricerche, Via Amendola 165/A, 70126 Bari, Italy; ^‡Ente per le Nuove Tecnologie l'Energia e l'Ambiente, C.R. Casaccia, Sezione BIOTEC-GEN.I-00060 Rome, Italy; and ^§Centre de Recherche en Infectiologie, 2705 Boulevard Laurier, Sainte-Foy, QC, Canada G1V 4G2

Edited by Patricia C. Zambryski, University of California, Berkeley, CA, and approved March 7, 2005 (received for review October 20, 2004)

Abstract

The function of the virion-associated protein (VAP) of cauliflower mosaic virus (CaMV) has long been only poorly understood. VAP is associated with the virion but is dispensable for virus morphogenesis and replication. It mediates virus transmission by aphids through simultaneous interaction with both the aphid transmission factor and the virion. However, although insect transmission is not fundamental to CaMV survival, VAP is indispensable for spreading the virus infection within the host plant. We used a GST pull-down technique to demonstrate that VAP interacts with the viral movement protein through coiled-coil domains and surface plasmon resonance to measure the interaction kinetics. We mapped the movement protein coiled-coil to the C terminus of the protein and proved that it self-assembles as a trimer. Immunogold labeling/electron microscopy revealed that the VAP and viral movement protein colocalize on CaMV particles within plasmodesmata. These results highlight the multifunctional potential of the VAP protein conferred by its efficient coiled-coil interaction system and show a plant virus possessing a surface-exposed protein (VAP) mediating viral entry into host cells.

Footnotes

↵ † To whom correspondence should be addressed. E-mail: l.stavolone{at}ba.ivv.cnr.it.
↵ ¶ Present address: University of Basel, Botanical Institute, Plant Health Unit, CH-4056 Basel, Switzerland.
Author contributions: L.S. designed research; L.S., M.E.V., and D.L. performed research; M.E.V. contributed new reagents/analytic tools; L.S., M.E.V., D.L., and T.H. analyzed data; and L.S. and T.H. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ATF, aphid transmission factor; CaMV, cauliflower mosaic virus; MP, movement protein; SPR, surface plasmon resonance; VAP, virion-associated protein.