June 30, 1998 University of California, Davis, biologists have brought a seed-building gene to life in a plant's leaves instead of its blossoms, a novel feat that could lead to valuable innovations in food crops.
The biologists first isolated LEC1, a widely sought gene believed to be key to seed development. Then they engineered plants that would put the gene to work much earlier than usual in the plant's life cycle.
One result of the gene's rescheduled activity was particularly striking: Some leaf surfaces sprouted tiny clusters of glove-shaped, embryonic tissue. And some of those embryos, while still attached to the leaf surfaces, even grew roots.
The new research, described in the June 26 issue of the journal Cell, was the work of researchers in the laboratory of UC Davis plant biologist John Harada and collaborators at UC Berkeley and UCLA. It was led by Tamar Lotan, a post-doctoral researcher with Harada.
"The discovery of LEC1 is very exciting," said Terry Thomas, a plant biologist at Texas A&M University who was not involved in the study. "It's an important step toward understanding the complex problems of seed development."
Harada said LEC1 will be useful in figuring out the coordination between the early, tissue-building stage of embryo development and the late, seed-maturing stage.
"The LEC1 gene is teaching us a great deal," he said. "And the research also has implications for some important applications."
For instance, making LEC1 function in a plant's leaves could revolutionize the production of oils and proteins from corn, canola (rapeseed) and soybeans -- essential food supplies for people and livestock.
"Mature seeds contain lots of those oils and proteins. They nourish the developing plant in the period after the seed germinates and before photosynthesis begins," Harada said. "Traditionally, we've had to wait for those products a long time -- until the plant matures, blooms and sets seed.
"But there may be advantages to engineering a plant that produces them in its vegetation," he said. Imagine, for example, grinding corn leaves instead of corn kernels for cooking oil.
Another possibility is that plant embryos might be raised in leaf-tissue nurseries to solve a long-standing problem in agriculture: how to more efficiently produce plants with the qualities and vigor that are now achieved only by cross-breeding, or hybridization.
For many crops, hybrid seed is generated by crossing different elite lines, each selected for desired traits. However, these hybrid offspring don't consistently pass those qualities down to their offspring.
But embryo farming could produce "artificial seeds" that would all be clones of the hybrid parent and perpetuate its strengths, said Harada and another author of the study, biologist Bob Goldberg of UCLA.
"If the LEC1 gene paves the way to the development of seeds without fertilization, it would have enormous potential," Goldberg said. "Hybrid vigor could be fixed in a given line, making it unnecessary to cross inbred lines and establishing a hybrid generation after generation. That would provide a new strategy for significantly increased yields in food and fiber production."
Harada stresses that those are all applications that might become possible, but haven't yet. "The results in this study were promising, but technically difficult to achieve," he said.
To wit: Of 7,000 seeds with the engineered LEC1 gene, only about 40 germinated. Ten of those seedlings grew stems and leaves and bloomed; seven set seed. Offspring from two of these plants had embryo-like structures on their leaves.
Next, the LEC1 researchers will explore the activities of the gene inside plant cells. The Cell paper establishes LEC1 (named for a mutation that affects a sprout's first leaves, called cotyledons) as an important regulatory gene, one that turns other genes on or off. Now the group wants to find out what those other genes are and what they do.
The group also hopes to show how LEC1's protein product interacts with other proteins to assemble seeds.
"We don't know that this work will definitely lead to applied uses," Harada said. "But if it does, it will be another example where beneficial applications come out of basic research -- in this case, basic research into plant embryogenesis and how it's regulated."
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