# Transcriptomic Analysis of the Candidate Genes Related to Aroma Formation in _Osmanthus fragrans_
); xcl27@foxmail.com (C.X. ); shitingtingting313@163.com (T.-T.S. ); 18694976599@163.com (G.-W.C.)  
2 College of Forestry, Nanjing Forestry University, Nanjing 210037, China 2  
Yong-Wei Chen  
1 College of Landscape Architecture, Nanjing Forestry University, Nanjing 210037, China; yangxl339@sina.com (X.-L.Y. ); tarashiyumi@163.com (H.-Y.L. ); yueyuanzheng@nifu.edu.cn (Y.-Z.Y. ); ruguoaiduideren@163.com (W.-J.D. ); xcl27@foxmail.com (C.X. ); shitingtingting313@163.com (T.-T.S. ); 18694976599@163.com (G.-W.C.)  
2 College of Forestry, Nanjing Forestry University, Nanjing 210037, China 2  
Yong-Wei Chen  
1 College of Landscape Architecture, Nanjing Forestry University, Nanjing 210037, China; yangxl339@sina.com (X.-L.Y. ); tarashiyumi@163.com (H.-Y.L. ); yueyuanzheng@nifu.edu.cn (Y.-Z.Y. ); ruguoaiduideren@163.com (W.-J.D. ); xcl27@foxmail.com (C.X. ); shitingtingting313@163.com (T.-T.S. ); 18694976599@163.com (G.-W.C.)  
1 College of Forestry, Nanjing Forestry University, Nanjing 210037, China 2  
Yong-Wei Chen  
1 College of Landscape Architecture, Nanjing Forestry University, Nanjing 210037, China; yangxl339@sina.com (X.-L.Y. ); tarashiyumi@163.com (H.-Y.L. ); yueyuanzheng@nifu.edu.cn (Y.-Z. headspace-solid phase, gas chromatography-olfactory, and gas chromatography-mass. According to previous research, the main volatile constituents of sweet osmanthus are terpenoids [4]. The amount of concrete production of _O. fragrans_ increases, along with the flower opening, and is at the highest level at the full flowering stage and then decreases at the final flowering stage [4; 5; 6]. Terpenoids, the largest class of aromatic compounds, are derived from isopentenyl diphosphate and its homologous isomer, dimethylallyl pyrophosphate. They have been synthesized by different terpene synthases (TPSs) via the mevalonate (MVA), or methyl erythroid-4-phosphate (MEP) pathway [7]. The MEP pathway in plant cell plastids has been a key approach for the synthesis of monoterpenes and their derivatives [8]. Xu et al. [9] isolated and identified ten MEP pathway genes in sweet osmanthus. The release regularities of aroma were consistent with the circadian rhythms of the OfDXS2 and OfDHR1 expression patterns. The floral scent released from the flowers or leaves was closely related to the expression level of the TPSs [10; 11; 12]. The major floral volatiles, linalool, and its derivatives produced in _O. fragrans_ flowers, were encoded by OfTPS1, OfTPS2, and OfTPS3 [13]. Moreover, the dioxygenase cleavage step itself could generate volatile products. For example, carotenes were cleaved into \(\alpha\)-ionone and \(\beta\)-ionone by OfCCD1 in vitro assays [14]. Except for these, there is no further information available concerning the molecular mechanism of floral scent formation in _O. fragrans_. Transcription factors (TFs) are proteins combined with _cis_-elements to regulate gene expression both spatially and temporally. They are also involved in the whole process of plant growth and development. Increasing reports indicate that terpene synthesis is governed by transcriptional regulatory networks. In cotton, _GaWRKY1_, bound to the promoter of sesquiterpene cyclase, positively regulates gossypol biosynthesis [15]. _WRKY3_ and _WRKY6_ have been found to be related to volatile terpene production for defense against pests in tobacco [16]. _MYC2_, a basic helix-loop-helix TF, interacts with the DELLA protein to activate expressions of sesquiterpene synthase genes, _TPS21_ and _TPS11_, in _Arabidopsis_ inflorescence [17]. _MYB14_ participates in the regulation of volatile terpenoid biosynthesis preferentially via the MVA pathway in a confer tree species [18]. The bZIP (Basic Region-leucine zipper) transcription factor, HY5, interacts with the promoter of the monoterpene synthase gene, QH6, in modulating its rhythmic expression [19]. _Arabidopsis_ PAP1, an MYB (V-myb myeloblastosis viral oncogene homolog) TF, can increase the phenylpropanol-derived color and terpenoids in PAP1-transgenic roses, but the regulatory mechanism remains unclear [20].