Genetic engineering, also called genetic modification, is the process of manually putting a target gene (new DNA) into an organism so that the organism will have a desired trait. Genetic engineering only works if we know which gene or genes can define the desired trait. C4 photosynthesis is a very complex trait, including anatomical, regulatory and metabolic subtraits, therefore also called the C4 syndrome. Since the C4 trait is still not well identified, it is still a big challenge to implement C4 into C3 plants through classical genetic engineering.
Evolutionary engineering, also called directed evolution, is widely used for complex phenotype engineering in microbiology (where it is also called adaptive laboratory evolution) in cases where the interest traits are insufficiently understood on the genetic level. Evolutionary engineering mimics natural evolutionary process and alters genomic make-up of an organism by accumulating mutations over multiple generations. There are generally two steps: i) continuous culturing of an organism over multiple generations under a certain selection pressure, and ii) screening for the organism obtaining desired biological traits. We can tell evolutionary engineering is terribly time-consuming. Evolutionary engineering alone is also unlikely to achieve the transformation from a C3 to a C4 plant in limited time.
Within CEPLAS, we are combining genetic and evolutionary engineering to transform Arabidopsis plants towards C4 metabolism. An existing mathematical model of C3–C4 evolution is used to choose the most promising path towards this goal. Based on biomathematical simulations, we are engineering Arabidopsis thaliana plants that express the central carbon-fixing enzyme Rubisco only in bundle sheath cells (Ru-BSC plants). This restriction of Rubisco to only one cell type is characteristic for C4 metabolism and therefore gives the plants a head start into the desired direction. This modification will initially be deleterious. Mutagenized Ru-BSC plants are then screened for improved photosynthesis, and are expected to respond to imposed artificial selection pressures by evolving towards C4 anatomy and biochemistry.
Dr. Yuanyuan Li, Plant Molecular Physiology and Biotechnology, Heinrich Heine University Düsseldorf
Under the heading Planter’s Punch we present each month one special aspect of the CEPLAS research programme. All contributions are prepared by our young researchers.