Accumulation of Hydrogen Cyanide Contributes to Bitterness in <i>Lilium</i> Bulbs

Objective/Background Lilium species possess notable medicinal properties, but their use is often limited by a bitter taste that reduces consumer acceptance. The molecular mechanisms underlying this bitterness remain unclear. The aim of this study was to investigate the role of cyanide accumulation in the bitterness of Lilium bulbs, with a focus on cyanide detoxification by the β -cyanoalanine synthase ( β -CAS) enzyme. Methods Transcriptome sequencing was performed on three Lilium cultivars, a notably bitter Lilium brownii cultivar (YAO) and two nearly nonbitter Lilium davidii cultivars (LZ and KZ), to identify key genes involved in bitterness. This analysis led to the identification of β -cyanoalanine synthase as a candidate gene. The cyanide content was subsequently quantified in the bulbs of each cultivar, and in vitro enzyme activity assays were conducted to determine the catalytic function of β -cyanoalanine synthase. Results Compared with the other cultivars, the bitter cultivar presented significantly lower expression of the β-cyanoalanine synthase gene. Cyanide content analysis revealed that the bitter cultivar accumulated the greatest amount of cyanide, which was positively correlated with bitterness. Enzyme assays confirmed that β -cyanoalanine synthase catalyses the conversion of cysteine and cyanide into β -cyanoalanine, indicating its role in cyanide detoxification. Conclusion Reduced β -cyanoalanine synthase expression in the bitter cultivar leads to cyanide accumulation in bulbs, contributing to bitterness. These findings offer a molecular basis for improving Lilium taste through genetic modulation of β -cyanoalanine synthase expression.