Objective  Bombax ceiba is an important ornamental plant in southern China. The aim of this study on the gene expression differences of flower buds and flowers in different stages was to reveal the genetic regulation mechanism of flower color variation, and provide a scientific basis for the establishment of flower color directional breeding technology.

  Method  Taking the petals of dark-red-line and yellow-line flowers of B. ceiba at different developmental stages as materials, and the Illumina HiSeqTM 4000 was used for transcriptome sequencing. DESeq2 and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases were used to identify differentially expressed genes (DEGs) and enrichment pathways.

  Result  A total of 75 190 unique genes were obtained by sequencing, and 4 772 single genes could be annotated by public databases. Gene function enrichment analysis showed that genes were mainly enriched in basic function prediction, signal transduction mechanism and post transcriptional modification, protein folding, molecular chaperone and other pathways, etc. A total of 10 397 DEGs at different periods were obtained, which were significantly enriched in 29 biological pathways, mainly including photosynthesis, metabolic and plant hormone signal transduction pathways. Among them, there were 72 DEGs involved in the phenylpropanoid biosynthesis pathway, and 25 DEGs involved in carotenoid biosynthesis, flavonoid biosynthesis, phenylalanine metabolism, respectively. These pathways and genes were all related to the biosynthesis of anthocyanins. Another 4 DEGs were significantly enriched in the betalain biosynthesis. The results of qRT-PCR data verified the reliability of the transcriptome data.

  Conclusion  (1) The genes related to photosynthesis, metabolic pathways, plant hormone signal transduction pathways, flavonoid biosynthesis pathways, phenylpropane biosynthesis pathways and energy metabolism pathways may be involved in the development of petals. (2) The genes involved in flavonoid biosynthesis pathway are significantly highly expressed in the middle stage and bloom stage of dark-red line, which may be the main reason for the dark-red flower color. (3) Some family members of the key synthase genes of the carotenoid biosynthesis pathway are highly expressed in the bud and middle stage of yellow-flower line, which may be the main reason for the yellow flower color.