# Transcriptomic Analysis of the Candidate Genes Related to Aroma Formation in _Osmanthus fragrans_
## Discussion  
_Osmanthus fragrans_, \"RiXiangGui\", a traditional horticultural plant known for its floral scent, is widely planted in Asia, especially in southern and central China [24]. Owing to its appealing fragrance and, potentially, exploitable chemical substances, the flowers areextensively used to produce teas, foods, perfumes, and medicines [6]. However, little information is available to explain the transcriptional regulation of the floral scent genes. As far as we know, there have been only two previous transcriptome reports based on RNA-Seq technology on the Oleaceae family. Using an orange-red-flowered cultivar, \"YanhongGui\"of the \(O\). _fragrans_, the petal color, carotenoid content, transcriptome dynamics of flower buds, and expression of key genes for the carotenoids were \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Transcription Factors** & **Profile0** & **Profile1** & **Profile4** & **Profile6** & **Profile7** & **All Profiles** \\ \hline C2H2 & 3 & 2 & 1 & 0 & 2 & 234 \\ ERF & 56 & 88 & 50 & 21 & 50 & 193 \\ bHLH & 24 & 26 & 13 & 5 & 4 & 168 \\ MYB-related & 4 & 6 & 6 & 3 & 5 & 155 \\ NAC & 101 & 158 & 110 & 47 & 80 & 134 \\ WRKY & 3 & 4 & 41 & 7 & 24 & 112 \\ MYB & 18 & 13 & 24 & 9 & 19 & 96 \\ bZIP & 4 & 3 & 2 & 0 & 0 & 89 \\ GRAS & 2 & 0 & 8 & 11 & 15 & 82 \\ C3H & 0 & 1 & 0 & 0 & 2 & 73 \\ FAR1 & 3 & 6 & 11 & 6 & 10 & 67 \\ Dof & 11 & 3 & 2 & 0 & 1 & 59 \\ G2-Like & 3 & 0 & 1 & 1 & 1 & 56 \\ HD-ZIP & 0 & 1 & 0 & 0 & 0 & 52 \\ Trihelix & 4 & 2 & 2 & 0 & 3 & 50 \\ HSF & 2 & 1 & 0 & 1 & 0 & 43 \\ TCP & 6 & 11 & 2 & 0 & 7 & 41 \\ B3 & 6 & 11 & 10 & 8 & 8 & 40 \\ GATA & 14 & 10 & 0 & 1 & 3 & 34 \\ SBP & 4 & 5 & 0 & 0 & 0 & 32 \\ ARF & 0 & 2 & 2 & 1 & 1 & 29 \\ M-type & 4 & 3 & 11 & 5 & 7 & 22 \\ NF-YC & 0 & 1 & 0 & 0 & 0 & 16 \\ AP2 & 4 & 7 & 5 & 2 & 1 & 14 \\ CPP & 0 & 1 & 0 & 0 & 0 & 12 \\ WOX & 1 & 1 & 0 & 0 & 0 & 11 \\ LSD & 0 & 0 & 1 & 0 & 0 & 9 \\ YABBY & 1 & 1 & 0 & 0 & 0 & 8 \\ BES1 & 2 & 2 & 0 & 0 & 0 & 8 \\ SRS & 1 & 0 & 1 & 2 & 1 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The number of the transcription factors identified in the expression profiles. analyzed [25]. In our previous study, 197 and 237 candidate genes involved in fragrance and pigment biosynthesis, respectively, were functionally annotated [26]. Here, nine libraries were constructed to perform RNA-Seq, and 136,611 unigenes were generated with a maximum length of 16,876 bp, a minimum length of 201 bp, an average length of 792 bp, and an N50 length of 1424 bp. Due to the lack of available genetic information, only 47.43% of the unigenes searched against the Nr database were matched, suggesting that a large portion of the genes acting during blooming might involve some unique processes and pathways. The annotated unigenes of _O. fragrans_ showed the highest homology tothe unigenes of _Sesamum indicium_ (Figure S2), which may reflect a close evolutionary relationship between the two species. Plants release an array of secondary metabolites to adapt to changing environments throughout their life cycles. Floral volatile organic compounds are a relatively large group, which plays crucial roles in pollinator attraction, defense, communication, and interaction with the surrounding environment. They are classified into three major groups: Terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives [27]. Terpenoids are the largest class of floral volatiles and encompass 556 scent compounds [28]. Flower scents vary between plant species because their different relative proportions of volatile compounds. Within a species, the blend of emitted terpenoids differs quantitatively and qualitatively, with some compounds having common properties [29]. The \(\beta\)-ionone, _cis_-linaloid oxide (furan), _trans_-linalooxide (furan), and linalool were abundant in most _Osmanthus fragrans_ cultivars, with other compounds typically present in smaller amounts [4].