Genetic analysis reveals the inconsistency of amorpha-4,11-diene synthase, a key enzyme in the artemisinin synthesis pathway, in asteraceae

Abstract

BackgroundAmorpha-4,11-diene synthase (ADS) is a key enzyme in the artemisinin biosynthetic pathway. ADS promotes the first step of artemisinin synthesis by cyclizing faresyl pyrophosphate to synthesize the sesquiterpene product amorpha-4,11-diene. Thanks to the continuous improvement of genomic information, its evolutionary trace can be analyzed in a genome view.MethodsPhylogenetic analysis was used to identify ADS-like genes in other Asteraceae. Gene structure and motif analysis was used to analyze the structural similarity of these identified genes. Heterologous expression and GC–MS analysis were performed to determine whether the functions of ADS and Cna4666 are consistent. Validation of ADS genes evolutionary trajectories was achieved by selective pressure and synteny analysis.ResultIn this study, we extracted 8 ADS genes from the Artemisia annua L. genome annotation and 121 ADS similar genes from the genomes of Artemisia annua L. and other plants in the Asteraceae, and further exploring their evolutionary relationship. Phylogenetic analysis showed that the genes most closely related to ADS genes were found in the genome of Chrysanthemum nankingense. Among them, the gene structure and motif composition of Cna4666 is very similar to ADS, we wondered whether it has the potential to synthesize amorpha-4,11-diene. Therefore, we extracted the products of recombinant p0_ADS.1 and Cna4666 proteins by HS-SPME combined with GC–MS analysis, the results indicate that Cna4666 is an α-bisabolol synthase, which cannot synthesize amorpha-4,11-diene. Through synteny analysis, we did not find collinear blocks of ADS genes in the Helianthus annuus and C. nankingense genomes. Furthermore, Ka/Ks ratios indicated that the evolution of ADS genes from their similar genes principally underwent purifying selection, and there was a strong positive selection between ADS genes.ConclusionsThis study proved that ADS is a multi-copy gene in Artemisia annua L., and they are not widely distributed in Asteraceae. The data will increase our understanding of the evolutionary selection pressure on ADS genes. The results suggest that ADS genes are subject to strong positive selection internally, and it is possible that they are a recently evolved gene in the Artemisia.