## 3 Discussion
Linalool itself is one of the main produced floral volatiles, and the sequestration of linalool derivatives and the derivatives of the isoteric monoterpene alcohol geraniol were experimentally proved to be present in the floral organs of several plant species. The present study also indicates the possible involvement of wintersweet _CbpHLH_ genes in the signaling pathways of JA and GA, leading to the production of volatile floral terpenes. A similar phenomenon was reported in other plant transcription factors such as _AtPAP1_ in _Rosa hybrida_, WRKY in cotton (_Gossypium hirsutum_), ORCA3 in _Catharantthus roseus_, EF1 and ERF2 in _Atemisia annua_, and _AtMYC2_ in arabidopsis [20; 55; 56; 57; 58]. These transcription factors regulate the TPS genes by interacting with the DELLA proteins. The DELLA proteins act as a repressor of the TPS gene and negatively regulate the JA and GA signaling pathways by interacting with MYC2. An increase in the concentrationof JA and GA decreases the level of JAZ and DELLA proteins, thus releasing the MYC2 and inducing the TPS genes, which results in the production of more volatile compounds [20; 59; 60]. A combined application of JA and GA3 results in an increase in the expression of the TPS gene and volatile compound production in the transformed plants. Our findings are consistent with the previously reported experimental results where the application of MeJA induces monoterpene production and emits (E)-\(\beta\)-ocimine, \(\beta\)-myrrene, and a small increase in linalool in transgenic tobacco plants [60]. The plants transferred with the _CpbHLH13_ gene were found to increase sesquiterpene \(\beta\)-caryophyllene production in the arabidopsis and tobacco plants, and the expression of the genes _At5g23960_ and _At5g44630_, which are involved in the production of almost all the sesquiterpenes in the arabidopsis, was also higher than in non-transformed plants. It was previously reported that the arabidopsis gene _At5g23960_ is associated with the synthesis of humulene and \(\beta\)-caryophyllene, which together produce 43% of the terpene volatiles from the flower [49]. In addition to increase sesquiterpene (\(\beta\)-caryophyllene) production in the arabidopsis and tobacco plants, we also found a few transgenic tobacco plants (35S::_CpbHLH13_) showing reduced flower color compared with the wild type and those transformed by the empty vector pCAMBIA2300S (2300S-SR1). The results were also verified by measuring anthocyanin contents from the flower samples using a spectrophotometer. This significant decrease in anthocyanin production could be explained by the previously described function of the bHLH13 (JAM2) and bHLH17 (JAM1) transcription factors that act as the transcriptional repressors which negatively regulate JA responses resulting in anthocyanin reduction in transgenic plants [50; 51; 61; 62; 63]. Furthermore, it has also been reported that bHLH17 is a bHLH subgroup III transcription factor which acts as a transcriptional repressor after binding to the promoters of the target genes in the anthocyanin-regulating pathway [64], which antagonizes the activation function of MYC2 and TTS/MYB75 to negatively regulate JA responses including flowering and anthocyanin accumulation [61]. It has also been elucidated by a functional study that JAZ interacts with transcriptional activators such as MYC2 and MYB75, along with the transcriptional repressors bHLH13 and bHLH17, to reduce its transcriptional functions [61]. The balance between activators and repressors leads to an adequate output of JA responsive genes, which results in a suitable level of JA responses such as plant defense and anthocyanin accumulation. In this study, we characterized the functional aspects of two wintersweet bHLH transcription factors, _CpMYC2_ and _CpbHLH13_, for the production of volatile organic compounds.