1.13.17
POTENTIAL STRUCTURE OF CAPSID PROTEIN INVOLVED IN APHID TRANSMISSION

C JACQUET1, B DELECOLLE2, H LECOQ2, M RAVELONANDRO1 and J DUNEZ1

1Station de Pathologie Vegetale, INRA-Bordeaux, 33883 Villenave d'Ornon, France; 2INRA-Avignon, 84143 Montfavet, France

Background and objectives
Heteroencapsidation has been described for a long time in mixed infections involving different groups of aphid-borne viruses transmitted in a persistent or semi-persistent manner. So the exchange of capsid subunits between viruses of the same group can be responsible for the modification of vector specificity. Heteroencapsidation of a viral genome deficient for aphid transmission can lead to the change of its biological properties. Capsid protein (CP) produced in transgenic plants could be involved in such interactions [1]. Our objective was to verify the possible structures of CP capable of transencapsidating and to assist the aphid transmission of virus.

Results and conclusions
Four PPV CP gene constructs have been built. These constructs were first expressed in Escherichia coli to check the accumulation of pseudo-particles by electron miscroscopy. Virus-like particles (VLP) were found with the full-length CP (FLCP) and with a PPV CP lacking the DAG amino-acid triplet involved in aphid transmission. However, no VLPs were observed with CP lacking three respective amino-acid residues R220, Q221 or D264, known to be involved in the assembly of other potyvirus CP [2]. Transgenic Nicotiana benthamiana lines expressing the different PPV CP constructs were infected with a non-aphid-transmissible strain of zucchini yellow mosaic virus (ZYMV-NAT), and aphid-transmission assays demonstrated that ZYMV-NAT was only transmitted from plants expressing CP gene containing the DAG triplet recognized to be essential for this biological assistance.

References
1. Lecoq H, Ravelonandro M, Wipf-Scheibel C, et al., 1993. Molecular Plant-Microbe Interactions 6, 403-406.
2. Jagadish MN, Huang D, Ward CW, 1993. Journal of General Virology 74, 893-896.