SEQUENCE COMPARISON OF RNA2 OF NEMATODE-TRANSMISSIBLE AND NEMATODE-NON-TRANSMISSIBLE ISOLATES OF PEA EARLY-BROWNING VIRUS SUGGESTS THAT THEGENE ENCODING THE 29-KDA PROTEIN MAY BE INVOLVED IN NEMATODE TRANSMISSION

A cDNA clone containing the complete coding region of RNA2 of the newl y described TPA56 isolate of pea early-browning virus (English serotyp e, PEBV-E) has been obtained. A plasmid (pFLA56) containing this clone together with the 5' and 3' non-coding regions of PEBV isolate SP5 (t he type isolate of PEBV-E) and flanked by the CaMV 35S promoter and NO S terminator is infectious when co-inoculated onto plants with pCaN1, an infectious clone of PEBV SP5 RNA1. Virus containing RNA2 derived fr om the cDNA clone of the TPA56 isolate is transmitted by Trichodorus p rimitivus nematodes, whereas virus containing RNA2 from a clone of the SP5 isolate is not transmitted. Sequencing revealed 11 differences ou t of 3374 nucleotides between the transmissible TPA56 and non-transmis sible SP5 clones. However, only three of the base changes affected the amino acid sequences of virus gene products. A single, conservative a mino acid change was present in the virus coat protein. Two non-conser vative changes occurred in the protein of molecular mass 29.6 kDa expr essed from an open reading frame located downstream of the coat protei n gene, suggesting that it has a function in nematode transmission and that changes in this protein prevent vector transmission of the SP5 i solate of PEBV.