March 20, 2009

Unlike animals, plants don't have a fight or flight response to handle threats from their environment. But University of Nebraska-Lincoln research is showing they have the next best thing: the ability to adapt to hostile surroundings using a "genetic bag of tricks."

University of Nebraska-Lincoln plant geneticist Sally Mackenzie shows a tobacco plant that's been genetically modified to grow shorter and bushier. (IANR photo)

If plant geneticists can figure out how to manipulate these changes artificially, they may be able to develop crops suited to a variety of challenging growing conditions.

Ground zero for this research are the mitochondria found in both animals and plant. Mitochondria are home to a number of biochemical, developmental and genetic processes with crucial implications for cell function. Research has found significant differences between plants and animals in the scope of genetic activity that occurs in mitochondria, said Sally Mackenzie, UNL plant geneticist. "Where animals keep their genetic information in a very conservative way ... plants are unusually dynamic. They have all kinds of things happening," Mackenzie said.With changes in the mitochondria, plants "can grow in totally new ways," taking on different reproductive or growth strategies, the Institute of Agriculture and Natural Resources scientist added.For example, they might develop male sterility or grow variegated leaves, which are less appealing to herbivores. They might change their flowering times or grow more slowly and with a different habit in extreme drought. "Mother Nature has adapted this. It isn't just random," said Mackenzie, who directs UNL's Center for Plant Science Innovation.UNL researchers are trying to figure out what causes plants to do this, asking "Are there environmental things that would tell the plant 'you're in trouble?,'" Mackenzie said.It could be reaction to a lack of oxygen, excessive cold, salt stress or a potassium deficiency.At this point, researchers believe but don't know for certain that these changes are happening at the seed germination stage, Mackenzie said."We believe that germinating seeds actually may have the ability to sense their environment and, under certain conditions, when they're dropped in an environment that's really hostile, change their mitochondrial makeup to adapt" to their environment, Mackenzie said."We call it a genetic bag of tricks," said Alan Christensen, geneticist in UNL School of Biological Sciences, who's also involved in the research.

In the animal kingdom, of course, such evolution occurs, too, but it plays out over dozens of generations. In plants these genetic variations happen in the space of a single generation and the changes are stable, meaning they don't reverse themselves with the next generation.

Both broadleaf and grassy plants show this adaptability, Mackenzie said.

What makes perfect sense for plants to do to survive, of course, doesn't necessarily have agronomic value. For instance, some plants respond to drought by growing much more slowly and perhaps changing their flowering time.

Mackenzie and her research team — working with tomato, soybeans, tobacco, millet and sorghum — are "trying to figure out how Mother Nature turns this on."

So far, they've found they can get sweet sorghum to grow into a shorter, nonflowering, more fully branched, bushy habit. That might make it better suited to biofuel uses than traditional sweet sorghum.

They've even grown a sorghum with variegated leaves. "It looks like an ornamental, it's gorgeous," Mackenzie said.

The work grows out of earlier research in Mackenzie's lab in which she found a genetic key that enables scientists to develop male sterility in plants. Male sterile plants don't produce pollen, which makes it easier to breed improved hybrids that yield and perform better, and to produce hybrid seed more economically.

This Agricultural Research Division research by Mackenzie, Christensen and their team is funded by the National Science Foundation.

Dan Moser
IANR News Service