*2.6. Expression Patterns of RsAP2 Genes in Different Stages of the Flowering Process*

The heatmap of 115 RsAP2 genes (with 5 RsAP2 genes eliminated through the results of local Basic Local Alignment Search Tool, BLAST) was generated by the Fragments per Kilobase of Transcript per Million Mapped reads (FPKM) values, transformed by log2 (Figure 7). The RsAP2 genes had different expression patterns across the five development stages of *Rhododendron* flowers. Most of the RsAP2 genes had an especially high expression stage that was distinct from the others. Almost all of the RsAP2 gene clusters with tandem duplication events, such as RsAP2-5/6 and RsAP2-50/51/52, showed similar expression patterns, and they all had higher expression levels in the last flowering stage. Additionally, the cluster of RsAP2-80/81/82 had higher expression levels in the S1 and S2 stages but lower expression levels in other stages.

**Figure 7.** Heatmap of expression levels of RsAP2 genes in different development stages of *Rhododendron* flowers. The FPKM levels are transformed by log2 and labels of S1, S2, S3, S4 and S5 represent closed buds, buds showing color at the top but with the scales still present, initial flowering stage, full flowering stage and last flowering stage, respectively.

#### *2.7. Interaction Network Analysis of RsAP2 Proteins*

The protein interaction network referring to *Arabidopsis* orthologous proteins was constructed to speculate the relationship and synergy of RsAP2 proteins (Figures 8 and S1). According to the result, several RsAP2 genes represented to be core regulators to interact with other proteins. RsAP2-4 had high homology with AP2 protein in *Arabidopsis* and may be upstream from the regulatory network to affect various proteins. The Cytokinin Response Factor 2 (CRF2), CRF3 and CRF4 were determined to have pairwise interaction through the yeast two-hybrid system [31], and the corresponding RsAP2-54, RsAP2-76 and RsAP2-74 may have similar function in response to abiotic stress.

**Figure 8.** Partial interaction network of RsAP2 protein referring to orthologs in *Arabidopsis*.
