Yes, you can engineer plants to be more resistant to cold (a simple web search will pull up thousands of articles). But what you are really asking (I think) is, can we engineer plants to survive on the open surface of Mars? The answer to this is no, or at least not yet, but there are many researchers intrigued by the idea (e.g., http://www.astrobio.net/exclusive/3569/greening-the-moon-and-mars and http://www.nasa.gov/centers/goddard/news/topstory/2005/mars_plants.html). Part of the problem is that, although plants can survive some of the temperature swings that are seen on Mars, there are other factors that are more dire. Atmospheric pressure is a big one. The air pressure on the surface of Mars is less than 1/100th of Earth’s at sea level; sea level is 101KPa, and Mars’s surface is 0.7KPa. Many people are familiar with the fact that water boils at a lower temperature at high altitudes; this is because the atmospheric pressure is reduced the higher in elevation you climb. For instance, the top of Mt. Evans, in Colorado, is 14,265 feet (4,348 m). The pressure up there is 61 KPa, and water boils at 87 degrees Celsius, instead of the 100 degrees Celsius at sea level. On the surface of Mars, the atmosphere is almost 100 times less dense (0.7 KPa), and at this pressure, water “boils” as soon as it melts, so it is difficult to maintain the normal waterborne process in cells. This is where physics meets biology. Everything we know of needs liquid water at some point in its life cycle (even seemingly “dry” organisms, like lichens). The practical answer for growing plants on Mars in the near future is probably to use reduced-pressure greenhouses (e.g., http://gravitationalandspacebiology.org/index.php/journal/article/viewFile/1/1). An intriguing thought that is out of reach of our current molecular toolbox is to engineer a plant that can essentially create its own sealed microenvironment as it grows—fun stuff to think about.