Tobravirus 2b protein acts in trans to facilitate transmission by nematodes

Analysis of RNA2 of TRV PaY4 showed it to be recombinant, carrying 3'-termi nal sequences derived from RNA1. Virus produced using an infectious cDNA cl one ct PaY4 RNA2 was nematode transmissible, demonstrating that natural TRV recombinant isolates are not necessarily defective. Mutations introduced i nto PaY4 RNA2 showed that the 2b gene, but not the 2c gene, is required for transmission by both Paratrichodorus pachydermus and Fl anemones nematodes . Experiments examined whether infection of plants with two different Virus clones would impact upon nematode transmission of either virus. Simultaneo us inoculation with TRV crones expressing green or red fluorescent proteins revealed that mixing of the two virus populations did not occur, although, in roots, adjacent cells were found containing green- or red-tagged viruse s. Subsequently, in similar experiments it was found that a TRV PaY4 2b mut ant was transmitted when combined with wild-type TRV PaY4. Also, transmissi on of a 2b mutant of an in vitro TRV/PEBV recombinant virus (TRV-C1) occurr ed after coinfection with wild-type virus. Thus, the tobravirus 2b transmis sion protein is trans-acting. Although TRV PaY4 and TRV PpK20 are both tran smitted by P. pachydermus, a 2b mutant of TRV PaY4 was not transmitted when coinoculated to plants with TRV PpK20. (C) 2001 Academic Press.