Abstract
Lupins (Lupinus spp.) are nitrogen-fixing legumes that accumulate toxic alkaloids in their protein-rich beans. These anti-nutritional compounds belong to the family of quinolizidine alkaloids (QAs), which are of interest to the pharmaceutical and chemical industries. To unleash the potential of lupins as protein crops and as sources of QAs, a thorough understanding of the QA pathway is needed. However, only the first enzyme in the pathway, lysine decarboxylase (LDC), is known. Here, we report the transcriptome of a high-QA variety of narrow-leafed lupin (L. angustifolius), obtained using eight different tissues and two different sequencing technologies. In addition, we present a list of 33 genes that are closely co-expressed with LDC and that represent strong candidates for involvement in lupin alkaloid biosynthesis. One of these genes encodes a copper amine oxidase able to convert the product of LDC, cadaverine, into 1-piperideine, as shown by heterologous expression and enzyme assays. Kinetic analysis revealed a low KM value for cadaverine, supporting a role as the second enzyme in the QA pathway. Our transcriptomic data set represents a crucial step towards the discovery of enzymes, transporters, and regulators involved in lupin alkaloid biosynthesis.
Highlights
Lupins (Lupinus spp.) are minor legume crops that produce beans with a remarkably high protein content
quinolizidine alkaloid (QA) are an important family of plant-derived alkaloids with relevance to the chemical and agricultural industries
We report the first tissue-specific transcriptome profiling of a high-QA variety of narrow-leafed lupin (NLL)
Summary
Lupins (Lupinus spp.) are minor legume crops that produce beans with a remarkably high protein content (up to 40%). In the early 1930s, German and Russian breeders produced the first low-alkaloid varieties directly suitable for human and animal consumption (Ivanov et al, 1932; von Sengbusch, 1930). The introduction of these ‘sweet varieties’ paved the way for wider adoption in Europe and later in Australia, but at the same time resulted. Sweet varieties are not alkaloid-free, and the alkaloid levels in sweet beans vary greatly from year to year under field conditions, often surpassing the thresholds established by the food and feed industries (Cowling and Tarr, 2004). This variation is dependent on complex genotype–environment interactions yet to be unraveled (Cowling and Tarr, 2004)
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