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Mineral uptake and genetic diversity in rice


USA
November 18, 2014

researchers in rice field
Shannon Pinson and AgriLife plant physiologist Lee Tarpley (foreground), and technicians Richard Chase and Jerri Daniel (background) examine diverse rice lines found to have high concentrations of specific minerals in their grain. Photo: Stephen Ausmus, USDA-ARS.

Rice has been a staple of the human diet for several millennia, and it is especially common in the diets of developing countries. Unfortunately, rice grains lack many essential mineral nutrients, such as iron and zinc. As a result, people who depend on rice as a dietary staple often suffer from nutrient deficiencies.

In a study recently published online in Crop Science, Shannon Pinson and her collaborators examined the mineral concentrations in more than 1700 different varieties of rice. The study aimed to identify genetic factors that may control how these minerals accumulate in grains. Pinson is a USDA-ARS research geneticist at the Dale Bumpers National Rice Research Center, Stuttgart, AR.

The new study could ultimately help breeders develop rice varieties with enhanced nutritional value—a process known as biofortification. In contrast, genetically modified (GM) rice is created by artificially introducing genes into rice plants so that they can make certain nutrients not normally found in rice. But “to date, not a single GM rice variety has been commercialized,” says Pinson. As a result, it is important to determine whether biofortification can be accomplished through traditional breeding methods.

The search for genes that control traits not yet studied extensively requires the examination of as many varieties of rice as possible. “Rice is a highly divergent crop, grown under a very wide range of conditions around the world,” says Pinson. These conditions include deep flooding or dry soil, and extreme heat or cold. The new study looked at mineral concentrations of 1,763 rice varieties that originated from 114 countries.

researchers in flooded rice field
Rice growing in a flooded field at the Texas A&M AgriLife Research Center, in Beaumont, Texas. Scientists are studying the rice under both flooded and unflooded field conditions to see how differences in soil chemistry. Photo: Stephen Ausmus, USDA-ARS.

Pinson credits a technology known as “inductively coupled plasma mass spectrometry” (ICP-MS) for making a study of this magnitude possible. ICP-MS enables researchers to measure the concentration of many minerals in a sample containing as few as three kernels. This sensitivity allowed Pinson and her collaborators to grow very small plots of each rice variety they studied.

Minerals travel from soil into grains by a complex process. Root absorption is the first step. Next, minerals pass into the plant xylem—the vascular tissue that carries water and dissolved nutrients upward from the root. After that, some minerals are tied up in vegetative tissues. Others move from older leaves to newer ones and into developing grain. Each step of this process presents opportunities for genes to cause differences in eventual concentrations of minerals in the grain.

Pinson’s study lays the groundwork for understanding these genetic factors. “We found that some varieties accumulated higher grain concentrations of certain elements than other varieties. This happened on a consistent basis between fields and years,” says Pinson. These observed differences were not strongly driven by plant height or grain shape.

The grain concentrations of some minerals, like nickel and phosphorus, showed low heritability. However, most elements—including calcium, cobalt, and manganese—showed high heritability. In other words, breeders could use the genes associated with these “extreme” mineral concentrations to produce biofortified rice varieties.

Pinson and her coworkers are conducting additional studies to determine how many genes are involved in the extreme grain characteristics they observed. “The next step,” Pinson says, “is to identify molecular markers tagging these genes that have a major impact on grain nutritional value.” Once these markers are identified, breeders could use them to select for nutritionally enhanced rice varieties. If they are successful, consumers around the world could reap the benefits of biofortified rice.

From "Worldwide Genetic Diversity for Mineral Element Concentrations in Rice Grain." This article will be open access for 30 days after the publication of this news story.



More news from: CSSA - Crop Science Society of America


Website: http://www.crops.org

Published: November 18, 2014

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