To me, this is as remarkable a story as the history of vaccination in medicine.  And indeed, carrying the viral gene in essence “vaccinates” the papaya plant against the virus, only by a very different mechanism, which has only been understood recently.  Here’s how it works. A virus is simply a packet of genes in a protein coat (coat proteins are represented by green ovals). The first thing that happens when a virus is delivered into a plant cell by an insect is that the coat proteins are destroyed (1).  This releases the genes, which comandeer the cellular machinery, reprogramming it to make lots more copies of the genes themselves, represented by the wavy bars (2).  These then makes lots of new coat proteins (3) that then coat the viral genes to make new virus particles (4), waiting to be picked up by a new insect.  Meanwhile, they’ve pretty much wrecked the cells in which they replicate, eventually killing the whole tree. In transgenic resistant plants, the first step is the same: the virus takes takes off its coat protein.  But in the transgenic plants, the invading viral genes are recognized , and destroyed, preventing the virus from reproducing.  Is this something that happens in nature? Yes.  It is exactly how plants become immune to viral infection -- very similar to how you become immune to a disease once you’ve had it.  The next time it sees the same virus, your immune system recognizes it and destroys it.  So it is with plants:  once they’ve been infected by a virus, this mechanism allows them to resist reinfection.  What Gonsalves and his colleagues did, then, was figure out how to make the papaya trees immune to the ringspot virus by expressing just a little piece of the virus’s genetic information in the plant to make it think it had once been infected -- even though it hadn’t been.  He is considered a hero by the local farmers and has received national and internaltional awards for this work.  But he has also been attacked and villified for this work by people and groups who are against GMOs.