A promiscuous fatty acid ω-hydroxylase CYP94A90 is likely to be involved in biosynthesis of a floral nitro compound in loquat (Eriobotrya japonica)

Nitro groups are often associated with synthetically manufactured compounds such as medicines and explosives, and rarely with natural products. Loquat emits a nitro compound, (2-nitroethyl)benzene, as a flower scent. The nitro compound exhibits fungistatic activity and is biosynthesised from l-phenylalanine via (E/Z)-phenylacetaldoxime. Although aldoxime-producing CYP79s have been intensively studied, it is unclear what enzymes form nitro groups from aldoximes either in plants or in other organisms. Here, we report the identification of two cytochrome P450s that are likely to be involved in (2-nitroethyl)benzene biosynthesis in loquat through differential gene expression analysis using RNA-seq and functional identification using yeast and tobacco. CYP79D80 and CYP94A90 catalysed the formation of (E/Z)-phenylacetaldoxime from l-phenylalanine and (2-nitroethyl)benzene from the aldoxime, respectively. Expression profiles of CYP79D80 and CYP94A90 were correlated with the emission of (2-nitroethyl)benzene from loquat flowers. CYP94A90 also functioned as a fatty acid omega-hydroxylase as do other CYP94A fatty acid omega-hydroxylases. The CYP94As tested from other plants were all found to catalyse the formation of (2-nitroethyl)benzene from (E/Z)-phenylacetaldoxime. CYP79D80 and CYP94A90 are likely to operate in concert to biosynthesise (2-nitroethyl)benzene in loquat. CYP94A90 and other CYP94As are 'promiscuous fatty acid omega-hydroxylases', catalysing the formation of nitro groups from aldoximes, and are widely distributed in dicot plants.

Automated summary

Nitro groups are commonly found in synthetically manufactured compounds, but loquat emits (2-nitroethyl)benzene as a flower scent. Two cytochrome P450s, CYP79D80 and CYP94A90, are identified to likely catalyze the biosynthesis of (2-nitroethyl)benzene in loquat. CYP94A90 and other CYP94As are promiscuous fatty acid omega-hydroxylases that catalyze the formation of nitro groups from aldoximes in dicot plants.