Unravelling the biosynthetic pathway of quinolizidine alkaloids (QAs), regarded as antinutritional compounds of narrow-leafed lupin (NLL) seeds, is fundamental to best exploit NLL as food or feed. We investigated 12 candidate genes connected to QA biosynthesis, selecting them by transcriptomic and genomic approaches, from the landscape of genes differentially expressed in leaves of the high- and low-alkaloid NLL accessions. Linkage analysis enabled the assessment of the location of the candidate genes in relation to iucundus, a major locus of unknown identity, that confers reduced QA content in seeds. The key finding was the identification of APETALA2/ethylene response transcription factor, RAP2-7, cosegregating with the iucundus locus and located within a region with highly significant QTLs that affect QA composition. We additionally identified a 4-hydroxy-tetrahydrodipicolinate synthase (DHDPS) gene involved in L-lysine biosynthesis as being closely linked to iucundus. The distributed location of other remaining candidates (including previously known QA genes) across different linkage groups, also indirectly supports the transcription factor as a possible regulator of lupin alkaloid biosynthesis. Our findings provide crucial insight into QA biosynthesis in NLL. Additionally, we evaluated and selected appropriate reference genes for qRT-PCRs to analyse the expression levels of QA genes in NLL.

White lupin (Lupinus albus L.) has unexploited potential as a crop plant due to its high seed yield as well as protein and oil content in seeds. Wellcharacterized collections of gene resources are very important for breeding as a source of genetic variation. This paper presents the results of analyses for total content and qualitative composition of alkaloids in seeds of 367 L. albus accessions from the Polish Genebank. Accessions were divided into four classes of origin: wild collected material, land races, breeding lines, and cultivars. Apart from the expected broad variation as well as strong differentiation in the alkaloid content, a clear influence of domestication was observed. This was shown as an apparent decrease in the alkaloid content in breeding lines and cultivars classes. The total alkaloid content varies from 0.02 to 12.73% of the seed dry weight. Six major alkaloids (abundance [1%) were revealed: lupanine (28.22-94.49%, mean 76.06% in total content), 13-hydroxylupanine (0.10-32.78%, mean 8.23%), multiflorine (0.00-21.67%, mean 5.52%), albine (0.00-18.55%, mean 4.48%), angustifoline (0.24-12.14%, mean 2.07%), 11,12-seco-12,13-didehydromultiflorine (0.00-12.28%, mean 1.74%). Owing to its abundance, lupanine was found to be the most closely correlated to the total alkaloid content.

The total contents and qualitative compositions of alkaloids in seeds of 10 Old World lupin species (73 accessions) were surveyed using gas chromatography. The obtained results, combined with those for three lupin crops, Lupinus angustifolius, Lupinus albus, and Lupinus luteus, provide the most complete and up-to-date overview of alkaloid profiles of 13 lupin species originating from the Mediterranean Basin. The qualitative alkaloid compositions served as useful supplementary tools of species discrimination. On the basis of the most abundant major alkaloids, lupanine, lupinine, and multiflorine, the Old World lupin species were divided into four groups. Those containing lupanine (L. angustifolius, L. albus, and Lupinus mariae-josephi), containing lupinine (Lupinus luteus, Lupinus hispanicus, and Lupinus × hispanicoluteus), containing lupinine and multiflorine (Lupinus atlanticus, Lupinus palaestinus, Lupinus anatolicus, Lupinus digitatus, Lupinus pilosus, and Lupinus cosentinii), and containing multiflorine (Lupinus micranthus). Within a given group, certain species can be, in most cases, further distinguished by the presence of other major alkaloids. The discrimination of species based on the total alkaloid content was found to be less reliable because of the significant intra-species variations, as well as the influences of environmental factors on the seed alkaloid content.