Genome-Wide Identification, Classification, and Expression Profiling Reveals R2R3-MYB Transcription Factors Related to Monoterpenoid Biosynthesis in Osmanthus fragrans

Abstract

Osmanthus fragrans is widely grown for the purpose of urban greening and the pleasant aroma emitted from its flowers. The floral scent is determined by several monoterpenoid volatiles, such as linalool and its oxides, which are a few of the most common volatiles and the main components of the essential oils in most sweet osmanthus cultivars. In addition, the relative contents of cis- and trans-linalool oxide (furan) may affect the aromas and quality of the essential oils. MYB proteins represent the largest family of transcription factors in plants and participate in regulating secondary metabolites. Several cis-elements, especially AC-rich regions, are known to be bound by 2R-MYBs and could be found in the promoter of the enzyme genes in the terpenoid metabolic pathway. However, there has to date been no investigation into the 2R-MYB family genes involved in regulating terpenoid biosynthesis in O. fragrans. Here, 243 non-redundant 2R-MYB proteins were grouped into 33 clusters based on the phylogeny and exon-intron distribution. These genes were unevenly distributed on 23 chromosomes. Ka/Ks analysis showed that the major mode of 2R-MYB gene evolution was purifying selection. Expression analysis indicated that 2R-MYB genes in O. fragrans exhibited varied expression patterns. A total of 35 OfMYBs representing the highest per kilobase per million mapped reads in the flower were selected for quantitative real-time PCR analysis. The correlation analysis between the expression level and the contents of fragrant compounds at different flowering stages suggested that OfMYB19/20 exhibited remarkably positive correlation with the accumulation of cis-linalool oxides. OfMYB51/65/88/121/137/144 showed significantly negative correlations with one or more linalool oxides. Characterization of these proteins revealed that OfMYB19 and OfMYB137 were localized in the nuclei, but did not show transcriptional activation in the yeast system, which suggested that they may be bound to other transcription factors to exert regulatory functions. These findings provide useful information for further functional investigation of the 2R-MYBs and offer a foundation for clarifying the 2R-MYB transcription factors involved in the molecular mechanism of the regulation of monoterpenoid biosynthesis in Osmanthus fragrans.

Differential regulation of triterpene biosynthesis induced by an early failure in cuticle formation in apple

“…TFs from the R2-R3 MYB, WRKY, basic helix–loop–helix (bHLH) and ethylene-responsive factor (ERF) classes were differentially expressed in RU compared with GD. Of particular interest were MYB TFs as some MYBs have been linked to the regulation of both cuticle 41 and terpene biosynthesis 42 , 43 and, in apple, triterpenes are an integral part of cutin-associated and suberin-associated waxes 28 . A regularised canonical correlation analysis (rCCA) was performed to identify MYBs that were related to the production of specific types of triterpenes.…”

Evolution and functional diversification of R2R3-MYB transcription factors in plants

“…However, the nomenclature after R2R3-MYB is inconsistent, e.g. ~7% of studies refer to groups [ 62 , 63 ], ~31% refer to subfamilies [ 10 , 64 ], and ~54% refer to subgroups [ 23 , 65 ], with clade or cluster used occasionally [ 66 , 67 ]. Subfamilies and subgroups are the most common subsequent appellations after family.…”

Insights Into the MYB-Related Transcription Factors Involved in Regulating Floral Aroma Synthesis in Sweet Osmanthus

“…The number of OfMYB-related genes was more significant than that observed in other plants reported over the recent years ( Table 1 ; Jin et al, 2017 ), such as 109 genes in peach ( Zhang et al, 2018 ). In our study, we identified 212 MYB-related genes in O. fragrans , a value close to the number of R2R3-MYB genes in O. fragrans (243 genes) ( Li et al, 2020a ), thus representing the largest subfamily of MYB genes, which play critical roles in various processes of growth, development, and responses to abiotic or biotic stress. While high, the number of R2R3-MYB subfamily members did not exceed the number of 1R-MYB subfamily members.…”

“…Because of its pleasing floral fragrance and multitudinous flowers, sweet osmanthus is widely cultivated in China as a common landscape tree species ( Huang et al, 2015 ). Sweet osmanthus is relevant to several industries, including tea, food, and perfume production ( Li et al, 2020a ). The floral fragrance of sweet osmanthus has been comprehensively studied in terms of compound identification and classification.…”