The Color of Light

Sunshine, to our human eyes the light appears white, but buried within are all the colors of the rainbow. In order for you or I to detect the colors that compose white light we need help. Shining light through a prism is one way I know to separate light into its many colorful components. Plants, on the other hand, need no such help. They have proteins called photoreceptors that enable them to detect different wavelengths of light. There are several different types of photoreceptors. Phototropins sense blue light, phytochromes sense red light, and neochrome is a chimeric protein that has the ability to sense both blue and red light. 

Light, especially the blue and red portions, are the main types plants use to run their photosynthesis machinery. When taller plants shade out shorter plants they alter both the quantity and quality of the light that reaches the plants below. Thus it is important that plants can detect the light quality in order to respond appropriately, by either growing away from shady spots or altering how they develop. 

A few ferns hanging out with their mossy pals.

A recent study was published that literally sheds some light on the evolution of these light sensing photoreceptors. Neochromes, the light sensing proteins with dual abilities, are present in only two groups of plants, the green algae and the ferns. Previously, scientists thought that these two groups independently evolved neochromes. But this new research proposes a different explanation. They found that the hornworts, a small group of bryophytes, also have neochromes and their proteins are closely related to those in ferns. They are so similar in fact that they were most likely transferred from hornworts to ferns. 

Horizontal gene transfer is a pretty wild thing that can happen in biology. One organism, potentially distantly related to another, can transfer some of its genetic code to another organism. If it is helpful the organism will keep the new piece of DNA, use it, and pass it on to its offspring. Scientists think that neochromes were very useful for ferns. Growing in the shadows of taller flowering plants, neochromes enabled ferns to take full advantage of low light conditions, thrive, and diversify. I think the ferns should send a thank you note to the hornworts for that super useful gift. The transfer of neochromes from one to the other happened over 150 million years ago, but you know what they say, better late than never.

Fay-Wei Li, Juan Carlos Villarreal, Steven Kelly, Carl J. Rothfels, Michael Melkonian, Eftychios Frangedakis, Markus Ruhsam, Erin M. Sigel, Joshua P. Der, Jarmila Pittermann, Dylan O. Burge, Lisa Pokorny, Anders Larsson, Tao Chen, Stina Weststrand, Philip Thomas, Eric Carpenter, Yong Zhang, Zhijian Tian, Li Chen, Zhixiang Yan, Ying Zhu, Xiao Sun, Jun Wang, Dennis W. Stevenson, Barbara J. Crandall-Stotler, A. Jonathan Shaw, Michael K. Deyholos, Douglas E. Soltis, Sean W. Graham, Michael D. Windham, Jane A. Langdale, Gane Ka-Shu Wong, Sarah Mathews, and Kathleen M. Pryer. Horizontal transfer of an adaptive chimeric photoreceptor from bryophytes to ferns. PNAS, published ahead of print April 14, 2014, doi:10.1073/pnas.1319929111

Additional coverage of this research can be found at these links: National Geographic, ScienceDaily, and The Economist. 

For more on plant colors, check out Johnna's April edition of the Berry Go Round plant carnival. My favorite is the post about the iridescent fruits of Pollia condensate. Pretty cool that they are the shiniest living things on Earth!