Insect Resistance
Potato Beetle enjoys eating, as its name implies, potatoes. It's having a rather juicy meal here and you can see it does a pretty good job of devouring the plant. However, if the potato plant is carries a gene that prevents the beetle from eating it, it survives So, it's not just a fungi, it's also insects to deal with.
Controlling Plant Ripening
For some reason, it is quite easy to genetically engineer tomatoes. For years, people have been trying to figure out how to make better tomatoes, more resistant tomatoes. The press gets ahold of this idea and imagine more frivolous ideas of making a square tomato, presumably for the squareheads that will eat them. However, the real problem with tomatoes is the same problem that all vegetables and fruits have -- they rot.
This tomato is being attacked by a fungus which has threads penetrating through it, and really, from a fungus's standpoint, what it's trying to do is to make the food as distasteful to bigger animals as possible by introducing toxins into the vegetable making it inedible. So, there is a race that goes on between us, who want to eat the tomatoes, and the microorganisms that also want to eat it.
Now the problem is that vegetables and fruits ripen asynchronously so that they don't all get ripe at the same time. As a result, some are inevitably going to be lost to this rotting process and as much as 50% of a crop can be lost by rotting. One major goal is to develop a method of minimizing rotting.
How do you do that? Well, several laboratories, specifically that of Athanasios Theologis here on the west coast, figured out that there was a gene which gave rise to the gas ethylene which is produced by all of these vegetables and causes a vegetable to mature. We want to eat a tomato. The fungus wants to make it inedible to us. The plant simply wants it to ripen so that its seeds have food to allow further propogation. It's one of these three-party things and one desirable thing to do is to knock out the gene, the ACC synthase that makes ethylene. You see, you can not only add genes.....you can take them away.
  
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Winding Your Way Through DNA Resource Book Index
