American Scientist the Magazine of Sigma Xi, the Scientific Research Society

A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society

This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders These three carnivorous plants (clockwise from upper left) are Nepenthes singalana, Cephalotus follicularis and Utricularia praelonga. Although each has a cup-shaped leaf trap, the plants evolved independently. Biologists are searching for fundamen- tal development mechanisms that likely played a role. (Optical projection tomography images are courtesy of Karen Lee, Jerome Avondo, Grant Calder, Andrew Bangham and Enrico Coen at the John Innes Centre.)

3D Carnivorous Plants

Prominent molecular biologist Enrico Coen has discovered multiple classes of regulatory genes that are vital to the evolution and development of flowers. His research team—based at the John Innes Centre in England—is also investigating genes that produce plant leaves of specific sizes and shapes. To that end, Karen Lee, a researcher in Coen’s lab, is ramping up studies of carnivorous plants. Lee uses optical projection tomography (OPT), a relatively new type of microscopy, to get a better look at their growth and shape. Created to study gene expression in mouse embryos, OPT provides three-dimensional views of developing plants unavail- able from any other technology, Lee told American Scientist contributing editor Catherine Clabby.

Why are you interested in carnivorous plants? rotated. Computer software then assembles 3D images of These plants may help answer the question of how the full plant structures from the information obtained with vast variety of leaf and flower forms construct them- the detectors. selves from small groups of cells. Our team uses a combination of imaging, mathematical modeling and genetic What is the value of 3D imaging for this research? approaches to determine the rules by which genes con- For anything other than a growing linear file of cells or a flat trol the shaping of leaves and flowers. This approach sheet of expanding tissue, growth involves deformations in helps us understand mechanisms of leaf growth in the three dimensions. OPT allows us to compare and measure model plant species Arabidopsis thaliana, which has sim- such deformations as a complex leaf or flower develops ple leaves. Carnivorous plants are fascinating because and grows. With OPT we can also see inside a specimen. their leaves display complex shapes that allow them to And differences between mutants and normal leaves or entice, capture and devour animal prey. We would like flowers can be visualized more clearly using 3D images. to know how these shapes are generated and how they Gene expression patterns, visible with markers, are often evolved from species with simpler shapes. looked at in a slice of tissue on a microscope slide. But it can be difficult to know where this slice came from in a plant. Can such unusual plants be good model organisms? OPT overcomes this problem and allows us to see where a Bladderworts (Utricularia), Monkey cup pitcher plants gene is acting in the context of a whole organ, a functional (Nepenthes), the Albany pitcher plant (Cephalotus) and or structural unit in a plant. In carnivorous plants, that can other pitcher plant genera (such as Sarracenia and Darling- include bladders, the cup-like leaf structures that trap prey. tonia) all independently evolved cup-shaped leaves with lids. Common developmental rules may underlie these Will you combine gene expression and imaging studies? different forms. To get at the key developmental mecha- We plan to screen for Utricularia bladder mutations and nisms, we need a model carnivorous plant that is easy use OPT to compare mutant bladders with normal ones. to grow, image and genetically dissect. The bladderwort This will give us an idea of the role played by the gene Utricularia gibba is perfect. It has a tiny genome, which that was inactivated in the mutant. We intend to se- makes it amenable to sequencing and gene discovery. quence the genome of the mutant bladder and compare the sequence to the normal bladder genome to find the Why is it hard to observe plant growth and development? gene we have knocked out. Once we have the sequence It is challenging to capture how cells and tissues grow in of the mutant form of the gene, we can use it as a probe three dimensions (3D) and to quantify changing shapes to look at where the gene is expressed in slices of nor- through development. A plant must be kept alive and mal bladder tissue on microscope slides. OPT of whole growing while being imaged over many days. We use a bladders could allow these slices to be mapped to the combination of confocal and OPT microscopy, together whole bladder structure. This will give us clues to the with image analysis tools, to study plant development. role the gene plays in bladder developmental regula- Confocal microscopy captures growth of the molecular tory networks. Information obtained in this way will skeleton within cells and tracks cell growth and divi- help us understand how genes control bladder growth sion in developing primordial structures. But because it and how they differ from genes controlling growth of focuses a laser beam to a fine point, it cannot be used on a simpler plant leaf. If we find simple rules underlying samples larger than 1 millimeter. OPT works by project- complex leaf formation in carnivorous plants, we may ing light through a specimen at multiple angles. A detec- find the general principles by which complex forms in tor captures the shadows produced as the specimen is both plants and animals arise.

In Sightings, American Scientist publishes examples of innovative scientific imaging from diverse research fields. www.americanscientist.org © 2013 Sigma Xi, The Scientific Research Society. Reproduction 2013 January–February 57 with permission only. Contact [email protected].