## 2 Results
### Expression Analysis  
In order to illustrate the correlation between necary development and gene expression of _CpCRC_ and the other four YABBY genes, also that of the necary development and the floral scent, heatmap analysis with the RNA-Seq database in DP, OF, and WP stages [27] and qRT-PCR were conducted using cDNA derived from DP, OF, LB, and WP to determine the expression profile of five YABBY genes and 11 floral scent related genes in the flower buds of different developmental stages in _C. praecox_ (Figure 1F,K,R,W). Almost no _CpDMAPP_ was detected in DP, OF, LB, and WP. The relative expression of one necary development related gene _CpCRC_ and the other four YABBY family genes (_CpFIL_, _CpYABBY2_, _CpYABBY5-1_, and _CpYABBY5-2_) and seven floral scent genes (_CpSAMT_, _CpIPP_, _CpGPPS1_, _CpGPP_, _CpHLS_, _CpTER3_, and _CpTERS5_) gradually increased in OF to LB and WP. The expression levels of _CpFIL_, _CpCRC_, _CpYABBY2_, _CpYABBY5-2_, and _CpTER3_ were the highest, and those of _CpGPPS1_ and _CpTERS5_ were the lowest in DP. The expression of _CpYABBY5-1_, _CpSAMT_, _CpIPP_, _CpGPP_, and _CpLIS_ in DP was higher than that in WP. The highest and lowest expression levels of  
Figure 4: Sequence alignment and phylogenetic analysis of YABBY proteins. (**A**) Sequence alignment of YABBY proteins in _C. praecox_ and _A. thaliana_. Conserved domains (Zinc finger domain and YABBY domain) are underlined in blue. Identical residues are highlighted in black and similar residues are highlighted in grey. Dotted line and asterisk represented the gap and the position of odd times of ten in protein sequence. (**B**) Phylogenetic analysis by Neighbor-joining (NJ) bootstrap analysis (1000 replications). AtINO (_A. thaliana_) and NyalINO (_Nymphaea alba_) as outgroup. The gene accession number is shown in Materials and Methods. Five different symbols in front of the protein name reprent the five YABBY protein of _Chimonanthus praecox_ in this study. CpGPPS2 and CpMYR1 were in LB and OF, respectively. The expression of CpFPPS in DP was similar to that in LB, higher than that in OF, and lowest in WP (Figure 5). According to the RNA-Seq database in DP, OF and WP stages, CpFIL, CpCRC, CpYABBY2, CpYABBY5-1, and CpYABBY5-2 have similar expression pattern. The expression level in DP was higher than that in OF and WP and the lowest in WP (Figure 6). To further clarify the correlation between the distribution characteristics of nectaries in three different round of petals and gene expression, the expression profile of five YABBY genes and five floral scent related genes in the innermost, middle, and outer petals in OF stages (Figure 1K) was detected using qRT-PCR. The expression level of 5 YABBY genes and five floral scent-related genes gradually decreased in the innermost to the middle and outer petals. The relative expression levels of CpFIL, CpCRC, CpYABBY2, CpYABBY5-1, and CpYABBY5-2 in the innermost petals were 1.78- to 5.38-fold, and 3.24- to 12.57-fold higher than that in the middle and the outer petals, respectively. The relative expression levels of floral scent genes (CpIPIP, CpGPPS1, CpGPP, CpLIS, and CpTERS5) in the innermost petals were approximately 1.65- to 10.25-fold higher than those in the middle petals and 1.76- to 78.85-fold higher than those in the outer petals (Figure 7). They all have significant difference between the relative expression level of CpFIL, CpCRC, CpYABBY5-1, and CpLIS in middle petals and that of in outer petals (Figure 7). Based on SEM results, for the sake of the relationship between the distribution characteristics of nectaries in the same round of petals and the gene expression, qRT-PCR was conducted using cDNA derived from the upper and lower halves in middle petals from DP, OF, and WP (Figure 1F,K,W) to further detect the expression profile of one mercury development related gene CpCRC, four YABBY family genes (CpFIL, CpYABBY2, CpYABBY5-1/2) and two floral scent genes (CpIPP and CpGPPS1). The relative expression of these five YABBY family genes and CpIPP had a similar expression pattern.