Coordinated and High-Level Expression of Biosynthetic Pathway Genes Is Responsible for the Production of a Major Floral Scent Compound Methyl Benzoate in Hedychium coronarium

Abstract

Methyl benzoate is a constituent of floral scent profile of many flowering plants. However, its biosynthesis, particularly in monocots, is scarcely reported. The monocot Hedychium coronarium is a popular ornamental plant in tropical and subtropical regions partly for its intense and inviting fragrance, which is mainly determined by methyl benzoate and monoterpenes. Interestingly, several related Hedychium species lack floral scent. Here, we studied the molecular mechanism of methyl benzoate biosynthesis in H. coronarium. The emission of methyl benzoate in H. coronarium was found to be flower-specific and developmentally regulated. As such, seven candidate genes associated with methyl benzoate biosynthesis were identified from flower transcriptome of H. coronarium and isolated. Among them, HcBSMT1 and HcBSMT2 were demonstrated to catalyze the methylation of benzoic acid and salicylic acid to form methyl benzoate and methyl salicylate, respectively. Methyl salicylate is a minor constituent of H. coronarium floral scent. Kinetic analysis revealed that HcBSMT2 exhibits a 16.6-fold lower Km value for benzoic acid than HcBSMT1, indicating its dominant role for floral methyl benzoate formation. The seven genes associated with methyl benzoate biosynthesis exhibited flower-specific or flower-preferential expression that was developmentally regulated. The gene expression and correlation analysis suggests that HcCNL and HcBSMT2 play critical roles in the regulation of methyl benzoate biosynthesis. Comparison of emission and gene expression among four Hedychium species suggested that coordinated and high-level expression of biosynthetic pathway genes is responsible for the massive emission of floral methyl benzoate in H. coronarium. Our results provide new insights into the molecular mechanism for methyl benzoate biosynthesis in monocots and identify useful molecular targets for genetic modification of scent-related traits in Hedychium.

HS–SPME–GC–MS and Electronic Nose Reveal Differences in the Volatile Profiles of Hedychium Flowers

“…A total of 42 volatile compounds were identified, and terpenoids were the main volatile contents in six Hedychium accessions, which is in agreement with previous studies [ 7 , 8 , 10 ]. Furthermore, linalool and ( E )-β-ocimene constituted 62.34% of the total volatiles in ‘ZS’, which is in line with the previous findings that linalool and ( E )-β-ocimene are the main floral volatiles of this species [ 43 , 46 ]. The HCA analysis data showed that 42 volatile compounds from Hedychium accessions could be categorized into four clusters, while Spearman analysis revealed that these VOCs had different degrees of correlation ( Figure 2 ).…”

Metabolite and Transcriptome Profiling Analysis Revealed That Melatonin Positively Regulates Floral Scent Production in Hedychium coronarium

“…Hedychium coronarium J. Koenig, commonly known as ginger lily, is an important ornamental/medicinal plant that is widely grown in tropical and semitropical regions of the world. Terpenoids (monoterpenes and sesquiterpenes) and benzenoids/phenylpropanoids are the main volatile components of H. coronarium flowers, and they are released in abundant amounts during the blooming period, which is consistent with previous reports (Yue et al, 2014(Yue et al, , 2021Ke et al, 2019;Zhou et al, 2021). However, the molecular regulatory mechanism of melatonin underlying floral aroma production remains unknown.…”

“…The glass bottle was stilled for 30 min, and then a polydimethylsiloxane (50/30 µm divinylbenzene/carboxen) fiber (Supelco) was injected into the glass bottle to trap volatiles for 30 min. Thereafter, the adsorbed volatile compounds were analyzed using a GC-MS system with an Agilent 7890A GC and Agilent 5975C MSD as previously explained (Yue et al, 2015(Yue et al, , 2021.…”

Auxin-Responsive R2R3-MYB Transcription Factors HcMYB1 and HcMYB2 Activate Volatile Biosynthesis in Hedychium coronarium Flowers

“…Moreover, their expression pattern positively correlated with flower development as well as with the emission of monoterpenes, and their encoded enzymes localize to plastids ( Yue et al, 2015 ). Our functional characterization indicated that HcTPS3 functions in ( E )-β-ocimene production, HcTPS5 functions in linalool production, and HcBSMT2 functions in methyl benzoate production ( Yue et al, 2015 , 2021 ). Analysis of previously generated RNA-seq data showed that six HcMYB family members were clustered in a group involved in regulating secondary metabolism.…”