Transcriptome analysis identifies key gene LiMYB305 involved in monoterpene biosynthesis in Lilium 'Siberia'

LiNAC100 contributes to linalool biosynthesis by directly regulating LiLiS in Lilium 'Siberia'

MAIN CONCLUSION

The transcription factor LiNAC100 has a novel function of regulating floral fragrance by directly regulating linalool synthase gene LiLiS. Lilium 'Siberia', an Oriental hybrid, is renowned as both a cut flower and garden plant, prized for its color and fragrance. The fragrance comprises volatile organic compounds (VOCs), primarily monoterpenes found in the plant. While the primary terpene synthases in Lilium 'Siberia' were identified, the transcriptional regulation of these terpene synthase (TPS) genes remains unclear. Thus, understanding the regulatory mechanisms of monoterpene biosynthesis is crucial for breeding flower fragrance, thereby improving ornamental and commercial values. In this study, we isolated a nuclear-localized LiNAC100 transcription factor from Lilium 'Siberia'. The virus-induced gene silencing (VIGS) of LiNAC100 was found to down-regulate the expression of linalool synthase gene (LiLiS) and significantly inhibit linalool synthesis. Conversely, transient overexpression of LiNAC100 produced opposite effects. Additionally, yeast one-hybrid and dual-luciferase assays confirmed that LiNAC100 directly activates LiLiS expression. Our findings reveal that LiNAC100 plays a key role in monoterpene biosynthesis in Lilium 'Siberia', promoting linalool synthesis through the activation of LiLiS expression. These results offer insights into the molecular mechanisms of terpene biosynthesis in Lilium 'Siberia' and open avenues for biotechnological enhancement of floral scent.

Genome-Wide Characterization of Differentially Expressed Scent Genes in the MEP Control Network of the Flower of Lilium 'Sorbonne'

Fragrance is an important feature of ornamental lilies. Components of volatile substances and important genes for monoterpene synthesis in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway were examined in this study. Twenty volatile compounds (2 in the budding stage, 3 in the initial flowering stage, 7 in the semi-flowering stage, 17 in the full-flowering stage, and 5 in withering stage) were detected in the Oriental lily 'Sorbonne' using gas chromatography-mass spectrometry. The semi- and full-flowering stages were key periods for volatile substance production and enzyme function. Sequence assembly from samples collected during all flowering stages resulted in the detection of 274,849 genes and 129,017 transcripts. RNA sequencing and heatmapping led to the detection of genes in the MEP monoterpene metabolism pathway. Through gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis, we extracted key genes (LiDXS2, LiLIS, and LiMYS) and transcription factors (in the bHLH, MYB, HD-ZIP, and NAC families) associated with the MEP pathway. Tissue localization revealed that LiDXS2, LiLIS, and LiMYS were expressed in Lilium 'Sorbonne' petals in the full-flowering stage. Genes regulating the 1-deoxy-D-X-lignone-5-phosphate synthase family of rate-limiting enzymes, involved in the first step of monoterpene synthesis, showed high expression in the semi- and full-flowering stages. LiDXS2 was cloned and localized in chloroplast subcells. The relative expression of terpene-related genes in the MEP and mevalonic acid pathways of wild-type and LiLIS/LiMYS transgenic Arabidopsis thaliana, and changes in chemical composition, confirmed that LiLIS/LiMYS regulates the monoterpene synthesis pathway. The results of this study provide a theoretical basis for the synthesis of lily aromatic substances and the cultivation of new garden flower varieties.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

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

Lily is one of the most important cut flowers in the world, with a rich floral fragrance. To further explore the fragrance emission mechanisms of lily cultivars, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and organic solvent extraction-gas chromatography-mass spectrometry (OSE-GC-MS) were used to unveil the volatile organic compounds (VOCs) and endogenous extracts of seven lily cultivars. Furthermore, real-time quantitative PCR (qRT-PCR) was used to determine the expression levels of two key genes (TPS and BSMT) related to the biosynthesis of monoterpenoids and methyl benzoate. The results show that forty-five VOCs were detected in the petals of seven lily cultivars, and the main compounds were monoterpenoids and phenylpropanoids/benzenoids. Dichloromethane was the best solvent for extracting the endogenous extracts of Lilium 'Viviana' petals and eighteen endogenous extracts were detected using dichloromethane to extract the petals of seven lily cultivars. Each compound's emission ratio (natural logarithm of the ratio of VOC content to endogenous extract content) was calculated, and linear regression analyses between emission ratios and boiling points were conducted. Significant linear negative correlations existed between the emission ratios and boiling points of compounds, and the regression equations' coefficients of determination (R2) were all greater than 0.7. TPS was expressed highly in 'Viviana', 'Pink News', and 'Palazzo', and BSMT was expressed highly in 'Pink News' and 'Palazzo'. Correlation analyses between the gene expression levels and the monoterpenoids and methyl benzoate contents found that the TPS expression levels have strong positive correlations with monoterpenoids content, while no correlations were found between the expression levels of BSMT and the contents of methyl benzoate. This study lays the foundation for research on the release patterns of VOCs in the flowers of Lilium, and the breeding of lilies for their floral fragrance.

LiMYB108 is involved in floral monoterpene biosynthesis induced by light intensity in Lilium 'Siberia'

We find that the MYB family transcription factor, LiMYB108, has a novel function to regulate the floral fragrance affected by light intensity. Floral fragrance determines the commercial value of flowers and is influenced by many environmental factors, especially light intensity. However, the mechanism by which light intensity affects the release of floral fragrance is unclear. Here, we isolated an R2R3-type MYB transcription factor LiMYB108, the expression of which was induced by light intensity and located in the nucleus. Light of 200 and 600 μmol m^-1 s^-1 significantly increased the expression of LiMYB108, which was consistent with the improving trend of monoterpene synthesis under light. Virus-induced gene silencing (VIGS) of LiMYB108 in Lilium not only significantly inhibited the synthesis of ocimene and linalool, but also decreased the expression of LoTPS1; however, transient overexpression of LiMYB108 exerted opposite effects. Furthermore, yeast one-hybrid assays, dual-luciferase assays, and electrophoretic mobility shift assays (EMSA) demonstrated that LiMYB108 directly activated the expression of LoTPS1 by binding to the MYB binding site (MBS) (CAGTTG). Our findings demonstrate that light intensity triggered the high expression of LiMYB108, and then LiMYB108 as a transcription factor to activate the expression of LoTPS1, thus promoting the synthesis of the ocimene and linalool, which are important components of floral fragrance. These results provide new insights into the effects of light intensity on floral fragrance synthesis.