Waist-high corn stalks laden with full-size ears; squash plants that don't sprawl over half your yard; a miniature tomato plant offering hefty red fruits to astronauts weary of freeze-dried food: these are just a few of the possibilities raised by new research at Washington State University.

Lead investigator Professor B.W. (Joe) Poovaiah and research associate Liqun Du have discovered a way to control the ultimate size of a plant. By altering a specific gene, they were able to change the size of the plant that grew from an experimental seed. Different alterations led to different size plants, showing that plants might be "size-engineered" to fit the needs of growers.
Their findings are reported in this week's issue of the prestigious journal Nature. WSU has applied for a patent on the process.

Poovaiah said size-engineered plants could be a potent tool against worldwide hunger.

"Dwarf plants use less water and are more resistant to wind and rain damage than normal-size plants," he said. "They devote a greater proportion of their energy to producing seeds or fruit rather than stems and leaves."

He compares his findings to the development, in the 1960s, of semi-dwarf wheat varieties that boosted Third World wheat production in what became known as the "Green Revolution."

Poovaiah and Du worked primarily with Arabidopsis, a member of the mustard family, but have found similar genes with the same function in every plant they have examined, including important crop plants such as peas and rice.

In addition to large-scale agriculture, other potential uses for dwarf plants include ornamental horticulture, home gardens and even the greening of space. Some of Poovaiah's earlier funding came from NASA, to develop plants that will grow well - but small - within the confines of a spacecraft, as a way to provide both oxygen and fresh food during long missions.

The gene described in the Nature article directs the plant to make a protein, dubbed DWF1 (for "Dwarf 1"), that is involved in the production of a plant growth hormone. Poovaiah and Du showed that the normal form of DWF1 is needed, along with calcium and a calcium-binding protein called calmodulin, for a plant to attain its full normal size. When they modified the gene in one way, the plant topped out at less than half of normal height. Greater modification stunted the plant even further. Eliminating the gene (and hence the protein) resulted in a ground-hugging rosette of leaves with very little vertical growth.

The DWF1 gene is just one of many genes that Poovaiah's lab has identified that function in the "calcium messenger system" in plants. Calcium has long been known to be crucial in animals for a wide range of processes, including muscle contraction and the generation of nerve impulses, but its functions in plant biology have been more elusive.

Over the past three decades, Poovaiah and his team have shown that calcium and calmodulin are just as important in the internal workings of plants.

In addition to controlling growth, Poovaiah says the calcium messenger system enables a plant to adjust to water stress, light, temperature and other environmental factors. In legumes, it also mediates the interactions between roots and bacteria that lead to the transfer of nitrogen from the air to the soil in a form that plants can use to build proteins and other compounds necessary for life. A gene that Poovaiah's lab discovered in 1995 has recently been shown to play a key role in this process, which is known as symbiotic nitrogen fixation.

Poovaiah is a professor in WSU's Department of Horticulture and Landscape Architecture and the Center for Integrated Biotechnology. The research described here was supported by grants from the National Science Foundation and U.S. Department of Agriculture. More information and photographs about Poovaiah's work can be found at his website, http://molecularplants.wsu.edu/calcium/.