Scientists Map Light-Sensing Structures

November 18, 2005 - 09:01

The ability to accurately sense light governs everything from seed germination, photosynthesis and pigmentation to patterns of growth and flowering. Now, University of Wisconsin-Madison scientists have obtained a detailed map of one of biology’s most important light detectors, a protein found in many species across life’s plant, fungal and bacterial kingdoms. Scientists can now find out the secrets of how plants, in particular, react to light, allowing for a host of manipulations that could have a big impact on agriculture.

According to the university, a team of scientists from UW-Madison report in the Nov. 17 issue of the journal Nature that they have obtained the crystal structure of a phytochrome from a bacterium, the first such light-gathering structure depicted for all of biology. The structure of the bacterial phytochrome, according to the report, suggests its architecture first arose a billion or so years ago in a common ancestor and is shared among not only bacteria but also plants and fungi.

“This is probably the most important light regulator in agriculture,” said Richard Vierstra, a UW-Madison plant geneticist and one of two collaborating senior authors of the Nature paper. “It tells plants when to germinate. It tells them where to grow to absorb the most light and to avoid competition. It tells them when to flower. It tells them when to die at the end of the growing season.”

“We can now start changing how phytochromes work in a rational way to improve how plants respond to light,” said first author, graduate student Jeremiah Wagner. “People have been trying to do this for a long time. Practically speaking, we can now try to re-engineer the vision system of a plant.”

According to Vierstra, there are many kinds of phytochromes found in every plant, and they exist in virtually all cells. They occur in greater concentrations in cells that respond directly to light, such as in root tips and new shoots. The phytochrome revealed by the Wisconsin team was derived from a microbe known as Deinococcus radiodurans, a bacterium renowned for its tolerance to ionizing radiation.

According to Vierstra, the phytochrome has the ability to store the light it has detected, initiating a response days after it is sensed. And, the memory allows the plant to predict where the light will come from each day and then measure the length of daylight so the plants will flower in the correct season.

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