Phenotypic Characterization and Transcriptomic Profiling of Ziziphus jujuba var. spinosa Seedlings Under ATP Treatment and Identification of a Novel Lupeol Synthase

The tender leaves of Ziziphus jujuba var. spinosa (sour jujube) are widely consumed in China as a health-promoting tea, with triterpenoids being identified as one of their core bioactive constituents. However, key genes in the triterpenoid biosynthesis pathway remain largely uncharacterized in this species. Here, adenosine triphosphate (ATP) treatment inhibited sour jujube seedling growth, induced leaf curling and marginal withering in partial seedlings, and elevated triterpenoid content in seedling aboveground tissues. Transcriptome analysis showed that most mevalonic acid (MVA) pathway enzyme genes were not significantly altered, while some were downregulated, and some enzyme isoforms were slightly upregulated. Combined genome and transcriptome analysis identified one slightly upregulated oxidosqualene cyclase (OSC) gene, ZsLUS, among 13 sour jujube OSC family genes. Heterologous expression in yeast confirmed that ZsLUS encodes a bona fide lupeol synthase with catalytic activity. These results indicate that ATP treatment enhances triterpenoid accumulation without uniformly upregulating MVA pathway genes, suggesting a sub-pathway-specific regulatory mode or post-transcriptional regulatory mechanism for triterpenoid biosynthesis in sour jujube seedlings. This work deepens our understanding of the mechanism of ATP action on sour jujube triterpenoid biosynthesis and provides new clues for deciphering triterpenoid biosynthesis and accumulation in sour jujube leaves.