Study finds how plants perceive light

Plants are coated with a network of light-sensing photoreceptors that detect different wavelengths of light.

Van Andel Institute and Washington University scientists have determined the molecular structure of one of these vital photoreceptors -- a protein is known as PhyB -- revealing a wholly different structure than previously known.

The findings of the study were published in the journal 'Nature'.

"Photoreceptors, such as PhyB, help plants sense and respond to the world around them by influencing life-sustaining processes such as shade avoidance, seed germination, determination of flowering time, and development of chloroplasts, which convert light into usable energy," said VAI Professor Huilin Li, PhD, co-corresponding author of the study. "Our new structure sheds light onto how PhyB works and has potential for a host of applications in agriculture, renewable energy, and even in cellular imaging."

Understanding the shape of PhyB is important because its structure directly impacts how PhyB interacts with other molecules to communicate shifts in light conditions and to help plants adapt by driving changes in gene expression. Previous research on PhyB provided only a truncated snapshot rather than a detailed rendering of the entire molecule.

To determine their near-atomic resolution image of PhyB, Li and study co-corresponding author Richard D. Vierstra, PhD, of Washington University, turned to one of the most studied plants on Earth -- a humble weed called Arabidopsis thaliana. This small flowering plant is an ideal model for research because it reproduces quickly, is small, and is easy to grow.

UsingVAI's high-powered cryo-electron microscope, or cryo-EM, the research team snapped nearly 1 million particle images of PhyB connected to its natural chromophore -- a molecule that absorbs a certain colour of light. They then narrowed the images down to 155,000, which they used to construct the full visualisation of PhyB's structure at a near-atomic level of 3.3 Angstrom.

Their work revealed a surprise: rather than the parallel structure described by earlier studies, they found a complicated 3D structure with both parallel and anti-parallel sections. The findings suggest that PhyB may amplify small changes in light-sensing chromophore molecules and drastically change its shape in response -- a move that communicates the availability of light to the plant.

The discovery is the result of more than a decade of collaboration between Li and Vierstra and revolutionises what we know about PhyB and phytochromes, the family of receptors to which PhyB belongs. Until now, it was believed that PhyB and other phytochromes likely were similar to those used by single-celled organisms, such as certain bacteria.