Turnip mosaic potyvirus resistance in Nicotiana benthamiana derived by post-transcriptional gene silencing

The coat protein (CP) gene of turnip mosaic potyvirus isolate ESC8 (TuMV-ES C8) was cloned and sequenced. Comparisons of the 867-nucleotide (nt) CP reg ion with those of 11 TuMV isolates showed 86.7-89.3% nucleotide identity an d 92.4-95.5% amino acid identity. The CP gene was cloned into a plant expre ssion vector and transformed into Nicotiana benthamiana plants via Agrobact erium tumefaciens-mediated leaf disk transformation. Progeny from R-0 lines was screened for resistance to TuMV-ESC8. Five of 29 tested lines showed T uMV protection in more than 50% of their progeny. Interestingly, some of th e resistant plants transformed with the CP gene of TuMV displayed mild mosa icism in the new growing leaves at the later stages of evaluation; but thes e mosaic symptoms disappeared when the leaves were fully expanded. Collecti ve data from steady-state RNA analysis and nuclear run-on assay of a line s howed that the resistance was RNA-mediated through the post-transcriptional gene silencing mechanism.