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Understanding Dormancy in Rice Leads to Discovery

14.11.2008
A South Dakota State University scientist has demonstrated for the first time that a weed called red rice gets its seed color and its ability to remain dormant from the same gene.

That discovery has important implications for both rice-producing and wheat-producing regions. If red color and dormancy in wheat are controlled by a single gene, it could mean that it will be more difficult to handle pre-harvest sprouting in white wheat varieties, for example.

Red rice, or weedy rice, is a major weed in rice-growing regions. Extensive work by assistant professor Xing-You Gu in SDSU’s Department of Plant Science suggests that a single gene helps regulate more than one trait in red rice, including dormancy and seed coat color.

Gu said weedy rice causes problems for rice growers worldwide, in part because it germinates at a later time than domestic varieties of rice. That delayed germination is a reflection of the plant’s dormancy trait — the major focus of Gu’s research.

Like the pre-harvested seed-head shattering mechanism assures that the seed bank in the soil will be replenished before grain is harvested off the field, the dormancy trait is important for survival because it assures that seed will remain viable in the soil until conditions are right for germination.

“The question is, why is red rice so difficult to control in rice-growing areas?,” Gu said.

“Based on my recent research, red rice is not only a red pigmentation issue. This gene is a transcription factor participating in the regulation of many pathways that could enhance weedy rice’s adaptability.”

“Transcription factors” are proteins that are necessary to read and interpret genetic instructions in DNA. Gu said they act, for example, as part of the plant’s machinery to turn transcription of certain genes on or off to allow changes in the plant’s development.

Gu said the association of dormancy and red seed coat, or pericarp, color isn’t in itself surprising. Wheat breeders are aware of the connection, for example. But until now, scientists have not been sure whether a single gene or more than one is involved.

“In common wheat there is a report of association between seed dormancy and red seed coat color,” Gu said, adding that red-colored wheat varieties are more dormant than white varieties. That means red-colored varieties are also more resistant to pre-harvest sprouting — a major problem for growers of wheat varieties worldwide.

“The question we haven’t answered yet is if the dormancy genes and the red color genes are the same gene or two closely linked genes,” Gu said.

Gu said that if the genes are only closely linked in wheat, breeders could use genetic tools to dissect the genes and use the dormancy gene to improve white wheat varieties’ resistance to pre-harvest sprouting. If they’re the same gene, however, then there is absolutely no way to use the dormancy gene without also getting the red seed coat color.

“We haven’t done similar research in wheat, but based on our research in weedy rice, the gene that controls red color also controls seed dormancy,” Gu said. “Our research will have a possible impact on seed science and seed development.”

Gu said one focus of his work in the future will be to look for homologous genes — those that confer similar characteristics due to shared ancestry — in crops such as wheat and barley.

Gu said that if wheat is like red rice, then wheat breeders would have to search for additional dormancy genes independent of genes that also regulate red seed coat color in order to improve the resistance to pre-harvest sprouting of white-colored varieties.

A part of Gu’s work involves map-based cloning on major quantitative trait loci, or QTLs. A quantitative trait locus is a region of DNA, though not necessarily a gene, that is closely associated with an observable characteristic or trait.

Gu and his graduate students also do fine-mapping of QTLs by dissecting and identifying which subsection is responsible for seed dormancy. That research will help scientists and plant breeders everywhere understand which genes are involved.

“Seed dormancy is one of the most important biological mechanisms,” Gu said.

“The trait is important for seed-bearing plants, but of the detailed biological mechanism, we know very little.”

The National Science Foundation and the USDA National Research Initiative supported Gu’s seed dormancy research.

Jeanne Jones Manzer | Newswise Science News
Further information:
http://www.sdstate.edu

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