Nematode transmission of tobacco rattle virus serves as a bottleneck to clear the virus population from defective interfering RNAs

D17 is a defective interfering RNA derived from RNA 2 of tobacco rattle tob ravirus (TRV) isolate PpK20. Tobacco was transformed with D17 cDNA fused to the CaMV 35S promoter. Upon infection of the transgenic plants with TRV is olate PpK20 or the serologically unrelated isolate PaY4, the transgenic D17 RNA started to accumulate at high levels and strongly interfered with accu mulation of wild-type (wt) RNA 2. When D17 transgenic plants infected with isolate PpK20 were used as source plants in nematode-transmission experimen ts, the vector Paratrichodorus pachydermus efficiently transmitted virus to healthy bait plants. However, the nematodes transmitted only the wt virus present in the transgenic source plants, whereas virus particles containing the abundant, accumulated D17 RNA were excluded from transmission. Evidenc e is presented that wt RNA 2 and D17 RNA are encapsidated in cis by their e ncoded CPs, which are known to be functional and nonfunctional in transmiss ion, respectively. This mechanism would result in defective interfering RNA s, which rapidly arise after mechanical transmission of the virus in the la boratory, being eliminated from tobraviruses under natural field conditions . Also this mechanism which acts with nematode transmitted virus isolates c ontrasts with that of vector-transmission of defective potyviruses and lute oviruses by wt helper viruses. (C) 1999 Academic Press.