Metabolome and transcriptome association study reveals biosynthesis of specialized benzylisoquinoline alkaloids in Phellodendron amurense.

OBJECTIVE: Benzylisoquinoline alkaloids (BIAs) have pharmacological functions and clinical use. BIAs are mainly distributed in plant species across the order Ranunculales and the genus Phellodendron from Sapindales. The BIA biosynthesis has been intensively investigated in Ranunculales species. However, the accumulation mechanism of BIAs in Phellodendron is largely unknown. The aim of this study is to unravel the biosynthetic pathways of BIAs in Phellodendron amurens. METHODS: The transcriptome and metabolome data from 18 different tissues of P. amurense were meticulously sequenced and subsequently subjected to a thorough analysis. Weighted gene co-expression network analysis (WGCNA), a powerful systems biology approach that facilitates the construction and subsequent analysis of co-expression networks, was utilized to identify candidate genes involved in BIAs biosynthesis. Following this, recombinant plasmids containing candidate genes were expressed in Escherichia coli, a widely used prokaryotic expression system. The purpose of this genetic engineering endeavor was to express the candidate genes within the bacteria, thereby enabling the assessment of the resultant enzyme activity. RESULTS: The synonymous substitutions per synonymous site for paralogs indicated that at least one whole genome duplication event has occurred. The potential BIA biosynthetic pathway of P. amurense was proposed, and two PR10/Bet v1 members, 14 CYP450s, and 33 methyltransferases were selected as related to BIA biosynthesis. One PR10/Bet v1 was identified as norcoclaurine synthase, which could catalyze dopamine and 4-hydroxyphenylacetaldehyde into (S)-norcoclaurine. CONCLUSION: Our studies provide important insights into the biosynthesis and evolution of BIAs in non-Ranunculales species.