## 4 Discussion
In contrast, _RcTPS_ genes in the subfamilies TPS-c and TPS-e/f contained more exons (between 10 and 14), likely because of the presence of an additional exon encoding the ancestral 200 amino acids of unknown function at the N-terminus [7; 18; 83]. Previously, the features of RcTPS proteins were found to be related to two domains, one each at the N-terminus (PF01397) and C-terminus (PF03936) [1; 84]. All RcTPS-a and RcTPS-b proteins contained the RRX\({}_{8}\)W motif at the N-terminus, a motif shared by monoterpene synthetases in angiosperms that is known to play an important role in monoterpene cyclization [3; 17]. None of the RcTPS-g members contained the RRX\({}_{8}\)W motif, since the prominent feature of this subfamily ofproteins is the rifeness of acyclic monoterepenes [3]. In addition, it was previously reported that TPS-g proteins can catalyze the biosynthesis of sesquiterpenes and diterpenes [85; 86]. The in vivo terpene synthase products mainly depend on their subcellular location and substrate availability [87]. The DDX motif was found in all RcTPS proteins. This motif plays an important role in cleaving premyl diphosphate substrates by binding the metal cofactor (Mg\({}^{2+}\) or Mn\({}^{2+}\)) at the C-terminus. In addition to the conserved RRX\({}_{8}\)W and DDX motifs, NSE/DTE was another important conserved motif at the C-terminus, whose function is the same as that of DDX [1; 14; 15]. NSE/DTE could be found in almost all RcTPS proteins of the subfamilies TPS-a, TPS-b, TPS-g and TPS-e/f. Expression analysis of _RcTPS_ genes in different rose tissues indicated that _RcTPS_ genes were mainly expressed in floral organs. _RcTPS17_, _RcTPS29_ and _RcTPS45_ were not expressed in any of the nine analyzed tissues at the analyzed stages, suggesting strict regulation of certain terpenoid biosynthesis genes in roses. Among the 26 _RcTPS_ genes with the highest transcript abundance in floral organs (Figure 7), 14 (_RcTPS01_, _06_, _08_, _11_, _12_, _14_, _16_, _22_, _23_, _26_, _27_, _34_, _36_, _44_) were predicted to encode putative sesquiterpene synthases, 10 (_RcTPS09_, _13_, _19_, _20_, _33_, _35_, _37_, _40_, _41_, _46_) encode putative monoterpene synthases, and 2 (_RcTPS02_ and _RcTPS31_) encode putative diterpene synthases. It has been reported in _R. chinensis_ that the contents of terpenoids are very low in flower buds. When the flowers open, the contents of terpenoids gradually increase and reach a maximum in open flowers, which is consistent with the trend of the transcript abundance of _RcTPS_ genes during flowering [88]. These data suggest that _RcTPS_ genes play essential roles in the biosynthesis of terpen in the flower opening process of _R. chinensis_. However, previous studies reported that in roses, _NULX1_ is involved in acyclic monoterepene biosynthesis [89; 34]. Although, NUDX and TPS pathways relay on a common precursor, namely GPP, the relationship between these two monoterepene biosynthesis pathways remains unclear. Increasing studies have shown that _TPS_ genes are involved in plant development and responses to biotic and abiotic stresses [1; 4; 72; 90]. It has been reported in many plant species that _TPS_ genes could be regulated by multiple abiotic stresses and that they may have important roles in resistance to abiotic stresses [24; 25; 26; 27]. Bioinformatics analysis identified multiple _cis_-acting elements that respond to abiotic stresses in the promoter region of _RcTPS_ genes, and the average number of _cis_-acting elements related to abiotic stresses in the promoter region of _RcTPS_ genes was eight, implying that they might have potential functions in response to abiotic stress. To verify this hypothesis, the expression patterns of _RcTPS_ genes under two abiotic stresses were analyzed. Because the water deficit and the associated osmotic stress as well as high-temperature severely limit the growth and flowering of _R.