C. RITZENTHALER - Nanobodies, a versatile tool to study plant viruses and much more

Abstract

Unlike most mammal antibodies, including human ones, camelid-derived Nanobodies (Nb) consist only of heavy chains, making them around a tenth of the size of conventional immunoglobulins. Nb offer the unique advantage to be monomeric, small, easy to produce, high thermostable and soluble. Their unique properties have triggered tremendous interests for research, diagnostic and therapeutics with applications covering numerous human diseases including cancer, Alzheimer's or viral diseases. In contrast, use of Nb in plant science remains so far limited.

Grapevine is a major target for viral diseases (Maliogka et al., 2015; Martelli, 2012). Already 64 viruses belonging to different genera and families have been reported for grapevine, but many more viral species are likely to be discovered. Unfortunately, no natural sources of resistance associated to viral diseases have been reported so far in Vitis species. Therefore, introgression of virus resistance genes into novel varieties as performed for other grapevine bioaggressors such as powdery or downy mildew and phylloxera are not accessible.

In collaboration with the group of Serge Muyldermans (VUB, Brussel), we have developed Nb against different grapevine viruses including Grapevine fanleaf virus (GFLV) and Arabis mosaic virus (ArMV) responsible for grapevine degeneration, a severe viral disease present in vineyards worldwide. These viruses related to human poliovirus are transmitted from grape to grape by ectoparasitic nematodes from the genus Xiphinema. Structurally, GFLV and ArMV are icosahedral viruses of 30 nm in diameter with a pseudo T = 3 symmetry composed of 60 identical subunits. In recent studies we have been able resolve the atomic structure of GFLV and identified surface-exposed structural motifs essential for GFLV transmission and movement (Amari et al., 2011; Lai-Kee-Him et al., 2013; Schellenberger et al., 2010; Schellenberger et al., 2011).

This talk will focus on the use of Nb for the detection of GFLV and ArMV  in vitro and in vivo. When fused to fluorescent proteins and expressed in plant Nb remain active and act as biosensors compatible with the spatio­temporal visualization of viral particles during the different steps of the virus life cycle including transmission and movement. Nb can also display powerful antiviral activity against GFLV and could therefore be of high biotechnological interest to confer resistance in grapevine. Evidence that links Nb-mediated resistance to vector transmission will also be provided. Finally, development of biosensors for the broad detection of viruses in plants and animal will be discussed.

References

Amari, K., Lerich, A., Schmitt-Keichinger, C., Dolja, V.V., and Ritzenthaler, C. (2011). Tubule-Guided Cell-to-Cell Movement of a Plant Virus Requires Class XI Myosin Motors. PLoS Pathog 7, e1002327.

Lai-Kee-Him, J., Schellenberger, P., Dumas, C., Richard, E., Trapani, S., Komar, V., Demangeat, G., Ritzenthaler, C., and Bron, P. (2013). The backbone model of the Arabis mosaic virus reveals new insights into functional domains of Nepovirus capsid. Journal of Structural Biology 182, 1-9.

Maliogka, V.I., Martelli, G.P., Fuchs, M., and Katis, N.I. (2015). Control of viruses infecting grapevine. Advances in Virus Research 91, 175-227.

Martelli, G.P. (2012). Grapevine Virology Highlights: 2010–2012. Proceedings of the 17th Congress of ICVG, 13-31.

Schellenberger, P., Andret-Link, P., Schmitt-Keichinger, C., Bergdoll, M., Marmonier, A., Vigne, E., Lemaire, O., Fuchs, M., Demangeat, G., and Ritzenthaler, C. (2010). A stretch of 11 amino acids in the ßB-ßC loop of the coat protein of grapevine fanleaf virus is essential for transmission by the nematode Xiphinema index. J Virol 84, 7924-7933.

Schellenberger, P., Sauter, C., Lorber, B., Bron, P., Trapani, S., Bergdoll, M., Marmonier, A., Schmitt-Keichinger, C., Lemaire, O., Demangeat, G., et al. (2011). Structural insights into viral determinants of nematode mediated Grapevine fanleaf virus transmission. PLoS Pathog 7, e1002034.

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