Quinolizidine Alkaloid Biosynthesis in Lupins and Prospects for Grain Quality Improvement

Abstract

Quinolizidine alkaloids (QAs) are toxic secondary metabolites found within the genus Lupinus, some species of which are commercially important grain legume crops including Lupinus angustifolius (narrow-leafed lupin, NLL), L. luteus (yellow lupin), L. albus (white lupin), and L. mutabilis (pearl lupin), with NLL grain being the most largely produced of the four species in Australia and worldwide. While QAs offer the plants protection against insect pests, the accumulation of QAs in lupin grain complicates its use for food purposes as QA levels must remain below the industry threshold (0.02%), which is often exceeded. It is not well understood what factors cause grain QA levels to exceed this threshold. Much of the early work on QA biosynthesis began in the 1970–1980s, with many QA chemical structures well-characterized and lupin cell cultures and enzyme assays employed to identify some biosynthetic enzymes and pathway intermediates. More recently, two genes associated with these enzymes have been characterized, however, the QA biosynthetic pathway remains only partially elucidated. Here, we review the research accomplished thus far concerning QAs in lupin and consider some possibilities for further elucidation and manipulation of the QA pathway in lupin crops, drawing on examples from model alkaloid species. One breeding strategy for lupin is to produce plants with high QAs in vegetative tissues while low in the grain in order to confer insect resistance to plants while keeping grain QA levels within industry regulations. With the knowledge achieved on alkaloid biosynthesis in other plant species in recent years, and the recent development of genomic and transcriptomic resources for NLL, there is considerable scope to facilitate advances in our knowledge of QAs, leading to the production of improved lupin crops.

Characterization of the genetic factors affecting quinolizidine alkaloid biosynthesis and its response to abiotic stress in narrow‐leafed lupin (Lupinus angustifoliusL.)

“…BBEs catalyse oxidative reactions, and Pictet–Spengler enzymes catalyse condensation reactions for the synthesis of alkaloids in other plant species (Cox & Cook, ; Facchini, Penzes, Johnson, & Bull, ; Kajikawa, Shoji, Kato, & Hashimoto, ; Samanani, Liscombe, & Facchini, ). These candidate QA biosynthetic genes may play a role in the formation of major QAs, such as lupanine and lupinine, from the intermediate Δ 1 ‐piperidine, or in further modification of QAs to yield a variety of structurally related compounds, for which most parts of the pathway are unknown (Frick et al, ). The genes identified by our transcriptomic and alkaloid gene cluster analyses represent good candidates for follow‐up analysis to further elucidate the QA biosynthetic pathway (Table S5).…”

Effects of two debittering processes on the alkaloid content and quality characteristics of lupin (Lupinus mutabilis Sweet)

“…For the calculation, 1 mL of 0.01 N H 2 SO 4 was equivalent to 2.48 mg of lupanin. The total alkaloid content was reported as the lupanin content, which is the most abundant alkaloid (55–66%) in the L. mutabilis species …”

Scientific opinion on the risks for animal and human health related to the presence of quinolizidine alkaloids in feed and food, in particular in lupins and lupin‐derived products

“…Although the Lupinus genus is a widely diverse family of plants, only four species are commercially cultivated as grain legume crops ( L. angustifolius , L. luteus , L. albus and L. mutabilis ). Of these, seeds (grains) of L. angustifolius are the most commonly used as feeds for livestock (Frick et al., ).…”