The use of cysteine proteinase inhibitors to engineer resistance against potyviruses in transgenic tobacco plants

As the processing mechanism of all known potyviruses involves the activity of cysteine proteinases, we asked whether constitutive expression of a rice cysteine proteinase inhibitor gene could induce resistance against two imp ortant potyviruses, tobacco etch virus (TEV) and potato virus Y (PVY), in t ransgenic tobacco plants. Tobacco lines expressing the foreign gene at vary ing levels were examined for resistance against TEV and PVY infection. Ther e was a clear, direct correlation between the level of oryzacystatin messag e, inhibition of papain (a cysteine proteinase), and resistance to TEV and PVY in all lines tested. The inhibitor was ineffective against tobacco mosa ic virus (TMV) infection because processing of this virus does not involve cysteine proteinases. These results show that plant cystatins can be used a gainst different potyviruses and potentially also against other viruses, wh ose replication involves cysteine proteinase activity.