## 4 Discussion  
Roses are highly appreciated ornamental plants, mainly for their flowers and delicate fragrances [33]. For many years, roses have been used in landscape greening, food, medicine, cosmetic production and especially as cut flowers [68; 69; 70]. However, roses often suffer from adverse unfavorable environmental conditions such as heat, salinity and drought. Plants produce specialized metabolites to adapt to their environments [71]. Volatile terpenoids play significant roles in resisting abiotic stress conditions [1; 4; 72]. In previous studies, phytoalexin terpenoids have been reported to accumulate in response to drought, salinity, ultraviolet and elevated CO2 stresses [73; 74; 75]. Additionally, floral terpenes were reported to protect reproductive organs from oxidative stress [76; 77]. Teprene syntheses play a leading role in catalyzing the formation of monoterpenes, sesquiterpenes, or diterpenes from the substrates GPP, FPP, or GGPP [3]. Previous studies on floral scent have mainly focused on the characterization and functional verification of the _TPS_ genes [78; 79; 80]. We show here that the expression of _TPS_ genes is modified in response to osmotic and heat stresses. As a mid-sized gene family, the number of genes in the TPS family in different plant species range from approximately 20 to 150 [3]. In this study, 49 _TPS_ genes were identified in the _R. chinensis_ genome based on BLASTP searches and two conserved TPS domains, and they were divided into five subfamilies (TPS-a, TPS-b, TPS-c, TPS-g and TPS-e/f) based on gene phylogenetic analyses. No members of the TPS-d and TPS-h subfamilies were found in this rose genome. These results are consistent with previous studies which showed that the TPS-d subfamily was specific to gymnosperms and that the TPS-h subfamily was only found in _S. moellendorffii_[3; 15; 18]. TPS-a is the largest subfamily among RcTPS proteins (34 of 49), followed by TPS-b (6 of 49), which is consistent with previously reported data in _A. thaliana_ (22 of the 32 _TPS_ genes were _TPS-a_ genes), _S. Iycopersicum_ (15 of the 34 _TPS_ genes were _TPS-a_ genes), _S. italica_ (21 of the 32 _TPS_ genes were _TPS-a_ genes) and _C. sinensis_ (28 of the 55 _TPS_ genes were _TPS-a_ genes) [18; 21; 24; 25]. Previously, the TPS-a subfamily was reported to be an angiosperm-specific clade, further divided into dicot-specific and monocot-specific subgroups, and that the TPS-a proteins are sesquiterpene synthases or diterpene synthases, while the TPS-b subfamily numbers are responsible for monoterpene or isoprene synthesis [3]. In _A. thaliana_, four TPS-a proteins are cytosolic sesquiterpene synthases, one is a mitochondrial sesquiterpene synthase, and the remaining TPS-a proteins are plasidial or mitochondrial diterpene synthases. Six _A. thaliana_ TPS-b proteins are monoterprene synthases that produce mycrene or octimee [18]. In _S. Iycopersicum_, all 15 TPS-a proteins have been reported to be sesquiterpene synthases [20]. In our study, 34 TPS proteins that all belong to the TPS-a subfamily in _R. chinensis_ were predicted to be sesquiterpene synthases, 10 RcTPS proteins were predicted to be monoterpene synthases, and 5 RcTPS proteins were predicted to be diterpene synthases by the Terzyme database [81]. The 10 putative monoterpene synthases contained 6 TPS-b and 4 TPS-g proteins, and the 5 putative diterpene synthases harbored 1 TPS-c and 4 TPS-e/f proteins. These findings indicate that TPS proteins within the same subfamily may share similar functions. However, further functional analyses are required to confirm this hypothesis. It was previously reported that plant _TPS_ genes generally exhibit conserved intron-exon structures [18; 19; 82]. In _R. chinensis_, we found that 39 out of the 44 _RcTPS_ genes of the subfamilies TPS-a, TPS-b and TPS-g contained 7 exons. Five of the remaining _RcTPS_ genes contained fewer exons, probably because of intron loss.