PhD defence by Alexandra Bianca Maimann
It is with great pleasure we announce the PhD defence of Alexandra Bianca Maimann.
All are welcome!
Title: Cyanogenic glucosides in legumes and a fruit tree - Multiplicity of functions in secondary as well as in primary metabolisms
Abstract: Unable to escape their predators, plants have developed a wide range of complex defense strategies throughout their millions of years of evolution. One significant class of direct defense strategies are plant specialized secondary metabolites. Included in this group are cyanogenic glucosides (CNglcs), which deter predators by facilitating the release of poisonous cyanide during an herbivore attack. Some of the world’s most economically important crop plants are cyanogenic, probably because being cyanogenic is an advantage against pests. However, cyanogenic crops also carry a risk of cyanide poisoning in humans and livestock and it is thus of key interest to comprehend and be able to regulate CNglcs in plants. To do this, it is first necessary to understand the enzymatic pathways surrounding them. In addition, CNglcs have more recently been shown to be involved in other critical plant functions, including carbon and nitrogen transport, which makes it of interest to understand their metabolism better. In this PhD thesis, CNglcs and the pathways surrounding them were studied in three plant species: Almond and lima bean, as well as low or non-cyanogenic varieties of common vetch.
Almond contains the CNglcs prunasin and amygdalin. Through transcriptome and metabolite analyses, we proposed genes involved in carbon and nitrogen transport through the so called non-toxic alternative turnover and a putative recycling pathway of CNglcs. Finally, we also identified a seed specific amygdalin hydrolase. Lima bean possesses two CNglcs: linamarin and lotaustralin. Via cloning experiments and investigation of gene clusters, we discovered that the second P450 enzyme in the biosynthesis pathway is from a CYP83 family unlike the model legume Lotus japonicus, where the P450 is from a CYP736 family. Additionally, the results suggest that a small clustered pathway for oxime-based metabolism, as present in the closely related common bean, has evolved to produce cyanogenic glucosides. This is supported by the restricted occurrence of cyanogenesis to the Lunatus and Polystachios clades of the genus. Common vetch seeds are used as a source of protein and minerals for animal feed, but their utilization is limited by their content of prunasin and vicianin as well as cyano-amino acids. Via metabolite analysis using HPLC, LC/MS, a heat map and clustering analysis we identified three lines with low content of cyanogenic compounds. Findings from this work give insight to feed security program and sustainable agriculture, by improving the protein‐rich common vetch as a feedstuff for monogastric animals and consequently for protein‐rich animal feed crops.
Supervisors
Professor Birger Lindberg Møller, University of Copenhagen
Associated Professor Raquel Sánchez-Pérez, University of Copenhagen
Assessment Committee
Associate Professor Mathias Pribil, University of Copenhagen (chair)
Associate Professor Markus Piotrowski, Ruhr-Universität Bochum, Germany
Senior Research Scientist Rubini Kannangara, Riverstone Biotech, Denmark