A BAHD acyltransferase contributes to the biosynthesis of both ethyl benzoate and methyl benzoate in the flowers of Lilium oriental hybrid ‘Siberia’

Abstract

Lily is a popular flower worldwide due to its elegant appearance and pleasant fragrance. Floral volatiles of lily are predominated by monoterpenes and benzenoids. While a number of genes for monoterpene biosynthesis have been characterized, the molecular mechanism underlying floral benzenoid formation in lily remains unclear. Here, we report on the identification and characterization of a novel BAHD acyltransferase gene that contributes to the biosynthesis of two related floral scent benzoate esters, ethyl benzoate and methyl benzoate, in the scented Lilium oriental hybrid ‘Siberia’. The emission of both methyl benzoate and ethyl benzoate in L. ‘Siberia’ was found to be tepal-specific, floral development-regulated and rhythmic. Through transcriptome profiling and bioinformatic analysis, a BAHD acyltransferase gene designated LoAAT1 was identified as the top candidate gene for the production of ethyl benzoate. In vitro enzyme assays and substrate feeding assays provide substantial evidence that LoAAT1 is responsible for the biosynthesis of ethyl benzoate. It was interesting to note that in in vitro enzyme assay, LoAAT1 can also catalyze the formation of methyl benzoate, which is typically formed by the action of benzoic acid methyltransferase (BAMT). The lack of an expressed putative BAMT gene in the flower transcriptome of L. ‘Siberia’, together with biochemical and expression evidence, led us to conclude that LoAAT1 is also responsible for, or at least contributes to, the biosynthesis of the floral scent compound methyl benzoate. This is the first report that a member of the plant BAHD acyltransferase family contributes to the production of both ethyl benzoate and methyl benzoate, presenting a new mechanism for the biosynthesis of benzoate esters.

Genome-wide identification of tea plant (Camellia sinensis) BAHD acyltransferases reveals their role in response to herbivorous pests

“…For example, an acyltransferase ( AT1 ) from Clade 4 in tobacco was found to be involved in the synthesis of phenolamides (PAs) as a chemical defense against herbivores [ 17 ]. The Clade 6 acyltransferase gene LoAAT1 can simultaneously synthesize the main aroma components ethyl benzoate and methyl benzoate from Lilium oriental flowers [ 14 ]. For tea plant, these volatiles not only are major components of tea aroma but also serve as early warning signals to activate the defense response of tea plants [ 25 , 54 , 55 ].…”

“…Due to the important biological functions of these substrates and their products, an ever-increasing amount of research has focused on the functional resolution of BAHDs in plants. Extensive accumulating evidences have demonstrated that the BAHD family is involved in a wide variety of biological processes, including but not limited to plant growth and development [ 11 , 12 ], fruit ripening [ 6 , 13 ], floral formation [ 14 , 15 ], and biotic and abiotic stress responses [ 16 – 19 ].…”

Determination of Volatile Organic Compounds and Endogenous Extracts and Study of Expression Patterns of TPS and BSMT in the Flowers of Seven Lilium Cultivars

“…Therefore, there are likely other types of BAMTs or BSMTs that are related to the synthesis of methyl benzoate in 'Viviana' and 'Tiber'. In addition, a study has shown that a BAHD acyltransferase gene LoAAT1 also contributes to the biosynthesis of methyl benzoate in the petals of Lilium 'Siberia'; the differential expression of this gene in different lily cultivars may also be a reason for the differences in methyl benzoate content among these cultivars [45]. We conducted correlation analyses between the relative expression levels of two genes (TPS and BSMT) in the petals of seven lily cultivars and the contents of VOCs and endogenous extracts (β-ocimene, linalool and methyl benzoate).…”

Characterization of Key Odorants in Lushan Yunwu Tea in Response to Intercropping with Flowering Cherry

“…Studies showed that α-farnesene acts as a signal to activate the expression of β-1, 3-glucanase (CsBGL) gene in adjacent undamaged tea leaves [56]. Methyl benzoate has a fruity odor and is a common floral volatile component found in more than 80 plants [57,58]. We speculated that benzaldehyde, α-farnesene, and methyl benzoate in flowering cherry may have allelopathic interactions with tea trees as major allelopathic compounds, which affect the metabolism of tea trees and prompt EG green tea trees to produce key volatile compounds with unique flower flavors (Figure 6).…”