Rice “Atlas” Could Help Feed World

by Abram Katz | January 28, 2009 1:09 PM | | Comments (2)

Rice.jpgYale researchers have compiled the first comprehensive genetic map of the rice plant, which eventually may multiply the harvest of the world’s staple grain.

The rice atlas should also make the study of wheat, sorghum, maize and other grains easier, said Timothy Nelson, professor of molecular, cellular and developmental biology at Yale and lead researcher.

Already Nelson and colleagues have found that rice is equipped with the right combination of cells to perform the most efficient form of photosynthesis — a finding no one expected.

The research was funded by the National Science Foundation and was published online this month in the journal Nature Genetics.

The virtual atlas contains data on the relative activity of each rice gene across 40 cell types.

Rice is relatively easy to study because it has a small genome of about 30,000 genes. Each cell of a rice plant carries the full complement of genes, which contain instructions on what proteins to make, and when.

nelson.jpg“From the first cell division there is differentiation, a specialization of cells that is key to the function and structure of the plant,” said Nelson (pictured).

Among the questions that Nelson and fellow scientists ponder, he said, is “What is a cell type, how they get there, and how can we take advantage of certain cell types.”

These are fundamental biological questions, with tremendous practical potential.

China consumes 135 million metric tons of rice a year; followed by India, 85 million; Egypt, 39 million; Indonesia, 37 million; and Bangladesh, 26 million metric tons. (A metric ton is 2,000 kilograms).

The United States consumed a mere 3.9 million metric tons in 2003 to 2004, according to the U.S. Department of Agriculture. Between 1961 and 2002, per capita consumption of rice increased 40 percent, based on figures in the department of agriculture’s Rice Yearbook. Rice supports approximately half of the world’s population.

Consequently, figuring out methods to increase the yield of rice, or Oryza sativa, is crucial to billions of people.

The genome of rice has been solved for several years, meaning that scientists know the entire sequence of DNA base pairs, including genes and segments of DNA whose functions are unknown.

Understanding what different cells are doing in rice as it grows is an important next step in understanding the plant.

Nelson and colleagues examined 40 cell types from the same plant at different stages of growth.

That includes cells in seedling roots, shoots, leaves and in germinating seed.
Researchers used a microscope to examine layers of cells topped by a thin sheet of plastic. Cells of interest were “micro-dissected” by beaming them with an infrared laser. The resulting burst of energy melted the plastic sheet, causing the cell to adhere. That way different cells could be harvested from a section of root, or the surface of a leaf.

The next step was to figure out what each type of cell produced, and in what quantity, at a particular time in the growing plant.

Researchers determined the cell products by intercepting RNA during the synthesis of proteins.

When a gene on a segment of DNA is activated, enzymes unwind the double helix, and the sequence of nucleic acids are translated into messenger RNA. Transfer RNA then gathers the appropriate amino acids, which are assembled into a protein at a ribosome.

By catching the messenger RNA, the scientists were able to determine what proteins were being produced. They basically collected and analyzed the messenger RNAs produced by each cell type in the atlas.

“We can say exactly what these genes are doing in different cell types,” Nelson said.
“We we can query any gene we’re interested in,” he said.

Some cells expressed a few as 6,000 genes, while others used up to 16,000 or so genes.

Out of this mass of information, Nelson and co-workers were able to discern patterns of protein production, metabolites, and interactions between the different molecules.

“We’re very excited about this. We can do data mining and see patterns,” he said, such as production of plant hormones, and the synthesis and transport of proteins.
Nelson said he is especially interested in plants that perform C4 photosynthesis. Other plants utilize C3 or CAM photosynthesis.

C4 photosynthesis allows plants to absorb and utilize carbon dioxide rapidly, meaning less energy is wasted, and the plant can withstand higher temperatures and strong sunlight.

The C4 process requires two types of cells working together, mesophyll cells and bundle sheath cells. Rice was thought not to have bundle sheath cells, but Nelson and colleagues found bundle sheath cells in their plants. If a way could be found to increase the activity of these cells, rice could be grown with far greater efficiency.

The International Rice Research Institute, a non-profit organization in the Philippines, is funding C4 research in the hopes of increasing the world rice crop. The IRRI’s goal is to develop C4 rice plants that can produce 50 percent more grain than current types, using less water and fertilizer.

Nelson said C4 research also has the potential to make biomass grasses economically feasible in the U.S.

Meanwhile, the search for cells continues. Nelson said he ultimately expects about 100 cell types to emerge from rice.









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Comments

Posted by: Ben [TypeKey Profile Page] | January 28, 2009 5:12 PM

These types of discoveries scare me. I am sure these people have great intentions and I applaud their work. However, now that we know so much about this process some big Agro company will use the information "for the good of mankind." So many lives can be altered. For everyones sake, I truly hope for the best?

Posted by: PR2 | January 29, 2009 8:37 AM

I believe a metric ton is 1,000 kg (not 2,000).

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