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Journal of Virology, June 2009, p. 5784-5795, Vol. 83, No. 11
0022-538X/09/$08.00+0     doi:10.1128/JVI.02267-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Virion Stability Is Important for the Circulative Transmission of Tomato Yellow Leaf Curl Sardinia Virus by Bemisia tabaci, but Virion Access to Salivary Glands Does Not Guarantee Transmissibility ^,

Piero Caciagli,¹ Vicente Medina Piles,² Daniele Marian,¹ Manuela Vecchiati,¹ Vera Masenga,¹ Giovanna Mason,^1, Tania Falcioni,² and Emanuela Noris^1*

Istituto di Virologia Vegetale, Consiglio Nazionale delle Ricerche, Strada delle Cacce 73, 10135 Turin, Italy,¹ Departament de Producció Vegetal i Ciència Forestal, Universitat de Lleida, Avda. A. Rovira Roure 191, 25198 Lleida, Spain²

Received 29 October 2008/ Accepted 18 March 2009

The capsid protein (CP) of the monopartite begomovirus Tomato yellow leaf curl Sardinia virus (TYLCSV), family Geminiviridae, is indispensable for plant infection and vector transmission. A region between amino acids 129 and 152 is critical for virion assembly and insect transmissibility. Two previously described mutants, one with a double Q129P Q134H mutation (PNHD) and another with a further D152E change (PNHE), were found nontransmissible (NT). Another NT mutant with a single N130D change (QDQD) was retrieved from a new mutational analysis. In this study, these three NT mutants and the wild-type (wt) virus were compared in their relationships with the whitefly vector Bemisia tabaci and the nonvector Trialeurodes vaporariorum. Retention kinetics of NT mutants were analyzed by quantitative dot blot hybridization in whiteflies fed on infected plants. The QDQD mutant, whose virions appeared nongeminate following purification, was hardly detectable in either whitefly species at any sampling time. The PNHD mutant was acquired and circulated in both whitefly species for up to 10 days, like the wt virus, while PNHE circulated in B. tabaci only. Using immunogold labeling, both PNHD and PNHE CPs were detected in B. tabaci salivary glands (SGs) like the wt virus, while no labeling was found in any whitefly tissue with the QDQD mutant. Significant inhibition of transmission of the wt virus was observed after prior feeding of the insects on plants infected with the PNHE mutant, but not on plants infected with the other mutants. Virion stability and ability to cross the SG barrier are necessary for TYLCSV transmission, but interactions with molecular components inside the SGs are also critical for transmissibility.

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* Corresponding author. Mailing address: Istituto di Virologia Vegetale, Consiglio Nazionale delle Ricerche, Strada delle Cacce 73, 10135 Turin, Italy. Phone: 39 0113977916. Fax: 39 011343809. E-mail: e.noris{at}ivv.cnr.it

Published ahead of print on 25 March 2009.

Supplemental material for this article may be found at http://jvi.asm.org/.

Present address: Settore Fitosanitario-Regione Piemonte, Environment Park, 10144 Turin, Italy.

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Journal of Virology, June 2009, p. 5784-5795, Vol. 83, No. 11
0022-538X/09/$08.00+0     doi:10.1128/JVI.02267-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.