We know that when animals undergo stress biochemical changes result, some of which may be situationally useful (such as increased alertness), and some of which may be deleterious if too frequent or too persistent (such as increased blood pressure). It turns out that plants have a biochemical reaction to stress, as well. Stress, for plants, tends to mean environmental conditions outside the range for which they evolved -- too hot, too cold, insufficient sunlight or moisture or CO2, etc.. A typical plant response to such conditions is to shut down its own metabolism, to stop growing and to stop producing seeds and pollen.
It's possible, in principle, to increase a plant's ability to withstand harsh environmental changes, either through traditional hybridization, smart breeding or, for more extreme cases, genetic modification. But such changes don't necessarily mean increasing a plant's tolerance for stress; a modified plant could still undergo metabolic shutdown in environmental conditions it could otherwise survive easily.
Botanist Wendy Boss and microbiologist Amy Grunden of North Carolina State University have come up with a way to increase a plant's ability to handle stress through the suppression of the plant's stress chemicals. This is done through the introduction of genes from Pyrococcus furiosus, an extremophile undersea microbe that regularly gets pushed from superheated volcanic vents to sub-freezing temperature open water and back -- and survives without injury or stress. Such anti-anxiety modification is a necessary first step to making it possible for plants to be manipulated to make them survive better during extended droughts, radical temperature shifts... or in greenhouses on Mars.
The desire to engineer plants that can withstand and even thrive in the thin atmosphere, low temperatures, extreme UV radiation, and other harsh elements within a greenhouse on Mars is the driver for this research, which is funded by NASA's Institute for Advanced Concepts. (More details about the work in progress can be found in this presentation -- PDF.) Such greenhouses -- a necessary part of any extended or permanent habitation on the planet -- would remained relatively controlled conditions, but would still be more extreme than is typically found on Earth. Nonetheless, Grunden and Boss are clear that they see the work as having direct application at home, as well:
If Boss and Grunden are successful, their work could make a huge difference to humans living in marginal environments here on Earth. In many third-world countries, says Boss, "extending the crop a week or two when the drought comes could give you the final harvest you need to last through winter. If we could increase drought resistance, or cold tolerance, and extend the growing season, that could make a big difference in the lives of a lot of people."
Unstated in the various articles about the research, but a clear implication nonetheless, is the potential application of this work to Earth plant species in conditions of severe, long-lasting ecosystem disruption driven by global warming. Obviously, there's no known way to introduce the complex set of genetic changes to a wild plant population in total; such an effort would be undesirable in any case, as these are the kinds of change one would wish to monitor in a lab first. But there may be certain ecosystems in which it is deemed critical to maintain the presence of particular types or family of plants, whether for reasons of culture, ecosystem balance, or food agriculture. Research to figure out ways to allow plants to live in controlled conditions on Mars will be of significant value in a world where we are unable to prevent extreme environmental changes due to climate disruption.