The plot of M. Night Shyamalan's movie 'The Happening' is that plants mysteriously start releasing a neurotoxin that causes people to kill themselves. Originally I thought it was too ridiculous, but maybe, just maybe, it is possible.
A new study by by Drs. Michael Poulter and Hymie Anisman and colleagues in the October 15th issue of Biological Psychiatry found that the DNA of people who committed suicide is altered epigenetically compared to people who died suddenly of natural causes.
Let me explain. The human genome has tens of thousands of genes, but not all are expressed in every cell. To make a muscle cell a muscle cell instead of a brain cell, the body 'turns off' certain genes. One of the processes by which our cells do this is called DNA methylation. The study of such processes is called epigenetics - the study of changes in gene function that may occur without modifying the gene sequence, often as a consequence of environmental exposures.
The study compared the brain tissues of those who had committed suicide to those from a control group who died suddenly, from heart attacks and other causes. They found that the DNA in the suicidal group's brain tissue was ten times more methylated. The gene being shut down was a neurotransmitter receptor that plays a major role in regulating behavior. This study shows that genetic and environmental factors may interact to produce specific and long-lasting changes in the brain. It's uncertain as to how much was 'innate' or 'genetic' and how much might have been altered due to their environments, meaning that it's possible the methylation occurred in response to an external stimulus.
So what does this have to do with 'The Happening'? Well, the way I see it, cells are somehow signaled which genes to turn on or off and when. If they are signaled, there must be some sort of chemical or combination of chemicals/hormones/etc which tells them to do this. Thus there may exist some neurotoxin that could cause people to kill themselves. While I highly doubt plants will produce such a compound, as Shyamalan's plot predicts, we could - and it's even possible we could make it extremely potent, so that people kill themselves suddenly upon exposure.
OK, so it's a bit of a stretch, but it's really the first thing I thought of when I read about this research. It's probably more directly useful for the opposite reason - developing some kind of anti-depressant which ensures those genes don't get methylated. But if people suddenly start killing themselves for no obvious reason, don't say I didn't warn you.