Seed ripening and quinolizidine alkaloid dynamics in Lupinus mutabilis: from gene activity to metabolites

Lupins are high‐protein feed and food crops, but most species synthesize toxic quinolizidine alkaloids (QAs). Sweet lupins have been bred for low alkaloid levels, yet occasional reversion to the bitter, toxic phenotype requires routine monitoring for food safety. Understanding QA biosynthesis, transport, and seed accumulation is crucial for developing lupins as reliable crops and for strategies aimed at reducing toxicity or valorising alkaloids. Eight major QAs were quantified during seed ripening in Lupinus angustifolius and L. mutabilis . Pearson correlation analyses explored relationships among alkaloids and informed a hypothesis on pod‐to‐seed transport, especially in L. mutabilis . Semi‐quantitative profiling of ten putative minor alkaloids complemented the study, and targeted transcriptomics measured expression of QA‐biosynthetic and candidate transporter genes in pods and seeds. Both species showed distinct temporal accumulation patterns of the eight major QAs. Correlation data supported the hypothesis that pods are the primary QA source, with subsequent translocation to seeds in L. mutabilis . Minor‐alkaloid profiling expanded the alkaloid spectrum. Transcriptomics revealed low QA‐biosynthetic gene expression in seeds but detectable transporter gene expression, consistent with pod‐derived QA import. The evidence indicates that QA synthesis occurs mainly in pods, followed by transporter‐mediated movement into seeds. Recognising pods as the QA source provides a knowledge‐based target for reducing seed toxicity or for exploiting alkaloid transport pathways in future lupin crop improvement.