1.11.34
CHANGES IN THE 5' NON-CODING REGION OF PLUM POX VIRUS IN CONNECTION WITH SYMPTOM DEVELOPMENT

L PALKOVICS, N KARAMOVA, D PRIBEK and E BALAZS

Agricultural Biotechnology Center, H-21 01 Godollo, PC Box 411, Hungary

Background and objectives
Plum pox virus (PPV) is a member of the Potyvirus genus. The genome of PPV is a messenger polarity RNA molecule of 9786 nt in length with a Vpg protein at the 5' end and a poly(A) tail at the 3' end. This genomic RNA has a single open reading frame which is translated into a large polyprotein. This polyprotein is co- and post-translationally processed into functional proteins. The protein translation starts at the second AUG, which is at nt position 147. The role of the 5' non-coding region in virus replication and translation initiation has been analysed in detail [1], but limited information is available on the contribution of this region in disease symptom development. It was shown that PPV having a deletion between nt 127-145 induces mild symptoms. Wild-type symptoms were recovered when a second site mutation was made [2].

Results and conclusion
By constructing an infectious full-length clone of PPV-SK68 (nucleotide sequence Accession No M92280) we were able to infect Chenopodium foetidum, Nicotiana clevelandii and Nicotiana benthamiana plants. On Nicotiana species the symptoms were clearly different and considerably milder than induced by the wild-type PPV-SK68. This symptom phenotype proved to be stable for up to 10 months. Using recombinant full-length PPV clones we have identified that the 5' end of the virus is responsible for the new symptom phenotype. Two nucleotide changes were identified in this region at nucleotide positions 94 (A-G) and 117 (A-C). These mutations are out of the highly conserved region of potyviruses. The effect of these mutations on virus replication and symptom development will be discussed.

References
1. Simon-Buela L, Guo SH, Garcia JA, 1997. Journal of General Virology 78, 2691-2699.
2. Simon-Buela L, Guo SH, Garcia JA, 1997. Virology 233, 157-162.