The first colonists on Mars probably won’t be humans. More likely, they’ll be plants. And the prototypes of these leafy pioneers are under development right now. As part of a proposed mission that could put plants on Mars as soon as 2007, University of Florida professor Rob Ferl is bioengineering tiny mustard plants. He’s not altering these plants so that they can adapt more easily to Martian conditions. Instead, he’s adding reporter genes: part plant, part glowing jellyfish — so that these diminutive explorers can send messages back to Earth about how they are faring on another planet.