Toward transgenic sustainable productivity increases in Miscanthus giganteus

Miscanthus × giganteus is a more chilling-tolerant C4 biomass feedstock in comparison to other phylogenetically-related C4 crops such as maize, sorghum or sugarcane (1, 2). Photosynthetic activity of C4 crops is limited by the amount of pyruvate orthophosphate dikinase (PPDK) and rubisco which restrain regenerate of phosphoenolpyruvate (PEP) (1, 3, 4). At the same time, photosynthetic efficiency is shown to improve under fluctuating light when photoprotection response time is accelerated by overexpression of zeaxanthin epoxidase (ZEP), violaxanthin deepoxidase (VDE) and Photosystem II subunit S (PsbS) (5). We hypothesize that alleviating rate limitation in C4 photosynthesis by PPDK and accelerating relaxation of photoprotection will significantly raise photosynthetic efficiency in Miscanthus. Although M. × giganteus fits the characteristics of an ideal bioenergy crop with the added advantage of minimal invasive potential, the propagation of this highly productive feedstock is limited by its triploid genome and the sterility of the plant (6). Traditionally, biolistic transformation of Miscanthus uses embryogenic calli induced from immature influorescences as the main transformation material (7) which can only be collected once a year. In this study, we established a M. × giganteus transformation system at the University of Illinois at Urbana-Champaign using microparticle bombardment (8) and demonstrated this transformation method using vectors encoding genes related photoprotection in plants and PPDK, respectively. In order to increase the availability of material for transformation, we are also developing a system to induce embryogenic callus from shoot apices of M. × giganteus. With these in place, we hope to obtain a more robust system to study the effect of photosynthetic genes in transgenic M. × giganteus. References 1. Long SP, Spence AK (2013) Toward Cool C4 Crops. Annu Rev Plant Biol 64(1):701–722. 2. Fonteyne S, et al. (2018) Physiological basis of chilling tolerance and early-season growth in Miscanthus. Ann Bot 121(2):281–295. 3. Naidu SL, Moose SP, Al-Shoaibi AK, Raines CA, Long SP (2003) Cold Tolerance of C4 photosynthesis in Miscanthus x giganteus: Adaptation in Amounts and Sequence of C4 Photosynthetic Enzymes. Plant Physiol 132(July):1688–1697. 4. Wang D, Naidu SL, Portis AR, Moose SP, Long SP (2008) Can the cold tolerance of C4photosynthesis in Miscanthus x giganteus relative to Zea mays be explained by differences in activities and thermal properties of Rubisco? J Exp Bot 59(7):1779–1787. 5. Kromdijk J, et al. (2016) Improving photosynthesis and crop productivity by accelerating recovery from photoprotection. Science (80) 354(6314):857–862. 6. Boersma NN, Heaton EA (2014) Propagation method affects Miscanthus×giganteus developmental morphology. Ind Crops Prod 57(M):59–68. 7. Ślusarkiewicz-Jarzina A, et al. (2017) Effective and simple in vitro regeneration system of Miscanthus sinensis, M. × giganteus and M. sacchariflorus for planting and biotechnology purposes. Biomass and Bioenergy 107:219–226. 8. Sobańska K, et al. (2019) Optimised expression cassettes of hpt marker gene for biolistic transformation of Miscanthus sacchariflorus. Biomass and Bioenergy 127:105255. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (Award Number DE-SC-0018254).