Investigation of Alkaloid translocation into lupin seeds
PhD defence by Sophie Lisa Otterbach
In Europe, the high consumption of meat and dairy products has caused a large demand for high-protein livestock feed. As legume agriculture is underrepresented in the European Union, there is currently a 70 % deficit of high-protein feed, which is imported mainly as soybean and soy meal. Lupins (Lupinus spp.) are valuable legume crops with great potential to reduce this deficit. Lupin seeds have been used traditionally as animal feed and have recently gained attention as human health product. However, the seeds contain toxic quinolizidine alkaloids (QAs), which act as anti-nutritional substances and lessen the value of the grain. QAs are mainly produced in the shoots of the plant and accumulate to high levels in the seeds. However, the precise origin of QAs in the seeds is not known. In my PhD project, I addressed the question of whether QAs in lupin seeds are transported, de novo synthesized or both. Using a combination of metabolite profiling, gene expression studies, and crossing experiments, I show that in situ biosynthesis either does not occur in seeds or occurs to very low levels (Chapter II). This suggests that most, if not all of the QA accumulation in the seeds is due to transport processes. Additionally, I aimed at identifying individual transporters involved in the long-distance translocation of QAs. The identity of these transporters is crucial for molecular breeding approaches that aim at reducing the accumulation of QAs in the seeds while retaining QAs in vegetative tissues for defense against herbivores. I selected 29 transporter candidate genes and tested them using plant extracts as transport substrates and Xenopus laevis oocytes as heterologous expression system (Chapter III). Unfortunately, I was unable to detect any QA import activity. However, I positively identified transport activities importing glutamate and exporting aspartate. Apart from presenting and discussing these experimental results, this PhD thesis also includes a General Introduction (Chapter I), where the background and long-term goals of my project are presented, and a General Discussion (Chapter IV), where new approaches for identifying QA transporter are discussed. This thesis represents a significant contribution to the emerging field of transport of plant specialised metabolites. My findings will contribute to the development of NLL varieties with altered QA accumulation levels in the seeds for safe consumption for humans and animals. Ultimately, this will contribute to attaining a sustainable production of vegetable protein in Europe.
Associate Professor Fernando Geu-Flores
Professor Emeritus Enrico Martinoia, University of Zürich
Associate Professor Stig Uggerhøj Andersen, Aarhus University
Professor Alexander Schulz, PLEN (chair)