Researchers at the Boyce Thompson Institute for Plant Research (BTI) on Cornell's campus report a breakthrough in understanding how plants perceive and respond to light.

The study is published in the Nov. 23 issue of the journal Science.

A research team led by Haiyang Wang, assistant scientist at BTI and adjunct assistant professor of plant biology at Cornell, reported that two highly related proteins, called FHY3 and FAR1, are central to the process of translating photons of light into physiological responses in the plant.

While the scientists conducted their study on Arabidopsis, a small flowering plant used heavily as a model for research, the findings also provide insights into how crop plants respond to light, which may lead the way for engineering crops to adapt to light exposure in various environments.

The paper focuses on how the far-red light spectrum is perceived by plants. Previous research has shown that when photoreceptors called phytochrome A are activated by far-red light, they move from the cytoplasm (the fluid that fills cells) into the cell's nucleus. Once in the nucleus, the phytochrome orchestrates the plant's physiological response to light.

The researchers discovered that FHY3 and FAR1, acting as transcription factors in the nucleus, directly bind to the cell's DNA and regulate the expression of genes that launch processes to move phytochrome A into the nucleus. When a plant lacks either FHY3 or FAR1, or both of them, less phytochrome A gets in the nucleus and the plant cannot respond properly to light signals, even though it perceives light signals, just as in a normal plant.

The researchers also show that as phytochrome A accumulates in the nucleus and starts the signaling process necessary for directing the plant's physiological responses to light, such as seed germination, stem elongation, leaf expansion and flowering, the expression of FHY3 and FAR1 genes declines. This decline creates a feedback loop that prevents over-accumulation of phytochrome A in the nucleus.

In the course of their research, Wang and colleagues were initially puzzled by the appearance of the amino acid sequences of the FHY3 and FAR1 proteins, as they resemble certain enzymes called transposases, which facilitate the insertion of movable pieces of DNA known as "jumping genes" into new parts of the genome. Their studies suggest that at some point in evolution, an ancient transposase may have evolved into a transcription factor, an evolutionary twist that is discovered here for the first time. The researchers believe the shift likely happened early in the evolution of flowering plants.

"This is the first case reporting empirical evidence that the switch of a transposase into a transcription factor could really happen, although it may take a long evolutionary time," said Wang.

Jumping genes -- also known as transposable elements -- were discovered by Nobel laureate Barbara McClintock, Ph.D. '27, and recent research suggests they may play a larger role than previously known in creating new genetic mutations that spur evolution. These newly derived transcription factors may have helped the successful colonization of flowering plants.

Daniel Ripoll, a research scientist in Cornell's Computational Biology Service Unit and a co-author of the Science paper, played a key role in building computational models of the proteins. Rongcheng Lin, a postdoctoral fellow in Wang's lab, was the paper's first author.

The study was funded by BTI, the Triad Foundation, the National Science Foundation, University of Texas at Arlington, the National Institutes of Health and Microsoft Corp.