Scientists have engineered tobacco plants to thrive in heat that would wilt the hardiest strains alive today. The technique, described in the current issue of Science, could someday be used to equip a variety of crops with the genetic know-how to survive in scorching climates.
Most flowering plants begin to suffer when the mercury rises past 35°C or so. Aside from drying out foliage, the heat slows down photosynthesis. But some plants, like cactuses, keep their solar panels running smoothly. What seems to be important in heat tolerance is the composition of lipids in the membranes of chloroplasts, organelles where photosynthesis turns light into chemical energy. For instance, some desert plants have fewer trienoic fatty acids in their chloroplast membranes than plants such as wheat and tobacco, which are chock-full of the lipids.
Probing this connection, Yuuki Murakami and colleagues at Kyushu University and Chiba University, both in Japan, decided to try switching off the production of trienoic fatty acids in plants susceptible to heat. The team outfitted tobacco plants with a gene that controls these fatty acids in the well-studied lab plant Arabidopsis. When the researchers silenced the control gene, the engineered tobacco plants had up to 85% less trienoic fatty acids in their chloroplasts than normal. To check out the effect on photosynthesis, the team cultured the transgenic tobacco seedlings in petri dishes at 36°C. The tobacco loved the heat. After 45 days, the transgenic plants weighed up to nine times more than normal plants. Even more remarkable, they photosynthesized faster at 40°C than at room temperature, although it's not clear exactly why. After 2 days at 47°C--comparable to summer in the Sahara--normal tobacco plants withered and died, but the transgenic plants survived.
The new work is the "best evidence yet" that lowering trienoic fatty acids in chloroplast membranes can help a plant tolerate heat, says Thomas Sharkey, a plant biologist at the University of Wisconsin, Madison. The next step is to test the technology in the field, says Anthony Hall, a plant breeder at the University of California, Riverside. He points out that life in soil is much more complicated than life in a cozy petri dish. But Hall agrees that helping plants tolerate heat is a worthwhile endeavor, especially with global warming tickling thermometers.