*5.7. Total RNA Extraction and Transcriptome Sequencing*

RNA was isolated from 300 mg of flower buds at S1 and S2 period under 19 ◦C and 23 ◦C treatment using the EasyPure Plant RNA Kit (Tiangen, Beijing, China). The quality of total RNA satisfied the standards 1.8 ≤ OD260/280 ≤ 2.2 and OD260/230 ≥ 1.8. Five μg of total RNA was employed for cDNA libraries preparation and RNA deep sequencing (6 G × 250 bp) by Novogene Biological Information Technology Company (Beijing, China). Three biological replications were performed for the transcriptome analysis. The FPKM (fragments per kilo base of exon per million fragments mapped) was used to estimate gene expression levels and identify differentially expressed genes among 2 d, 19 ◦C vs. 2 d, 23 ◦C, and 5 d, 19 ◦C vs. 5 d, 23 ◦C. The differentially expressed genes were analyzed according to the log2(ratio of abundance) threshold, the value ≥1.0 was defined as upregulation, and ≤−1.0 was defined as downregulation, along with FDR <0.001.
