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February 19, 2002

Compact plant could reveal molecular secrets to higher crop yields

WEST LAFAYETTE, Ind. – Using a compact green plant, Purdue University researchers are unraveling mysteries about how genes affect plant growth and learning possible ways to control growth that eventually could lead to higher crop yields.

The Purdue scientists cloned a gene in the plant Arabidopsis (ah-rah-baa-dop-sis) required for controlling development and shape of cells and tissue, said Daniel Szymanski, assistant professor of agronomy. The study detailing how a mutant form of the gene SPIKE1 affects plant development is published in the latest issue of The Plant Cell.

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"Ultimately things like organ shape and whole plant architecture are really important for crop yield in the field," said Szymanski, a molecular biologist. "The angle of the leaves defines how tightly you can pack plants in when you plant them. Root architecture controls the ability of plants to take up nutrients."

Szymanski and his research team cloned SPIKE1, and then they compared a mutant plant with a normal Arabidopsis. The shape and size of the leaves and roots were stunted in the plant with the mutated gene, spike1. This gave the scientists clues as to the gene's function in altering the plant's architecture.

"The phenotype of this mutant plant suggests that reorganization of the cytoskeleton is affected in the mutant," Szymanski said. "That is evidence that this gene is involved in controlling cell shape and organization of the tissue."

The cytoskeleton is the internal structure of the cell and determines the cell's shape. The shapes and sizes of cells determine the architecture of leaves and roots. Szymanski said that SPIKE1 is similar to a family of genes found in humans, worms and fruit flies that also regulate how signals are transmitted from the outside of the cell to the cytoskeleton to control cell shape and organization of the tissue.

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This research is an early step in discovering important answers about plant development, Szymanski said.

"Ultimately we'd like to change the activity either of this gene or other genes in the cytoskeleton control pathway in order to regulate growth and development," he said. "This could be achieved either through genetic engineering or breeding and selection".

Because the mutant spike1 is lethal to seedlings, using it to develop desirable plants wouldn't be possible, he said.

"We'd like to identify other components of the pathway in which this normal gene, SPIKE1, is involved, or modify the activity of this gene to increase lateral roots or the total amount of root surface area without having all these other adverse effects on growth," Szymanski said.

Little is known at this time about plant cell biology, he said, so the current long-term goal is to learn more about how genes affect the cell growth.

"If we want to genetically engineer cells to have different physical properties or different chemical composition, we need to learn a lot more about the basics of plant cell biology," Szymanski said.

Arabidopsis, often used by plant biologists as a research tool, is the perfect model plant for several reasons, he said. It has the same physiology as most crop species so information garnered from its study is transferable; research seedlings are small – 1-2 centimeters in diameter, so many can be grown in a small space; the lifecycle of the plant is short; and different examples of the plant are easily obtained.

"I can learn things in a year or two that would take me eight or 10 years to learn in another plant species," Szymanski said.

The U.S. Department of Agriculture and the National Science Foundation provided funding for this research.

Writer: Susan A. Steeves, 765-496-7481, ssteeves@aes.purdue.edu

Source: Daniel Szymanski, 765-494-8092, dszyman@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web sites:
Purdue Motility Group
Purdue plant biology program

NOTE TO JOURNALISTS: In addition to the photos listed, microscopic shots showing cell growth and development also are available by contacting Susan A. Steeves at the Purdue Agricultural Communication Service, 765-496-7481, ssteeves@aes.purdue.edu.

PHOTO CAPTIONS:
Daniel Szymanski, Purdue University plant cell biologist, looks at the small plant Arabidopsis that is helping him answer big questions about what controls the shape, structure and function of cells. (Purdue News Service Photo by Tom Campbell)

A publication-quality photograph is available at ftp://ftp.purdue.edu/pub/uns/szymanski.plantcells.jpeg

 

The plant on the left is a normal one-week-old Arabidopsis seedling. On the right is an Arabidopsis of the same age but containing a mutant gene that has caused smaller misshapen leaves. (Photo from research lab of Daniel Szymanski)

A publication-quality photograph is available at ftp://ftp.purdue.edu/pub/uns/szymanski.plantcells2.jpeg


ABSTRACT

The Arabidopsis SPIKE1 Gene is Required for Normal Cell Shape Control and Tissue Development

Jin-Long Qiu, Ross Jilk, M. David Marks,
and Daniel B. Szymanski

Regulated growth and cell shape control are fundamentally important to the function of plant cells, tissues, and organs. The signal transduction cascades that control localized growth and cell shape, however, are not known. To better understand the relationship between cytoskeletal organization, organelle positioning, and regulated vesicle transport, we conducted a forward genetic screen to identify genes that regulate cytoskeletal organization in plants. Because of the distinct requirements for microtubules and actin filaments during leaf trichome development, a trichome-based morphology screen is an efficient approach to identify genes that affect cytoplasmic organization. The seedling lethal spike1 mutant was identified based on trichome, cotyledon, and leaf-shape defects. The predicted SPIKE1 protein shares amino acid identity with a large family of adapter proteins present in humans, flies, and worms that integrate extracellular signals with cytoskeletal reorganization. Both the trichome phenotype and immunolocalization data suggest that SPIKE1 also is involved in cytoskeletal reorganization. The assembly of laterally clustered foci of microtubules and polarized growth are early events in cotyledon development, and both processes are misregulated in spike1 epidermal cells.


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