Transcriptome analysis reveals the molecular mechanism of flower bud development in Fritillaria pallidiflora

Flowering is an important turning point from vegetative to reproductive growth, and flower bud development plays a vital role in the life of ornamental plants. Despite progress in model plants, the molecular regulatory mechanisms underlying flower bud development remain unknown in the perennial ornamental bulbous plant genus Fritillaria L. In this study, gene expression profiles associated with flower bud development were comprehensively analyzed in Fritillaria pallidiflora to better understand the biological mechanisms underlying its floral development. Morphological observations allowed for differentiation into three different critical developmental stages (pre-differentiation stage: S1; bud differentiation stage: S2; and fully completed stage: S3), which were used for transcriptome sequencing. Based on transcriptomic profiles, 74,353 unigenes were assembled, 34,288 of which had protein functional annotation. A total of 3128 differentially expressed genes (DEGs) between sequential stages (S1 vs S2, and S2 vs S3) were identified, 1886 of which displayed a clear differential expression pattern at S2. Based on GO and KEGG pathway enrichment of the 1886 DEGs, 45 unigenes that might be related to floral bud differentiation were selected, including seven genes related to circadian rhythm, eight genes involved in carbohydrate metabolism, nine genes related to plant hormones, seven genes related to temperature, and 11 transcription factors. These results offer a valuable collection of gene expression profiles characteristic of flower bud differentiation in F. pallidiflora. These DEGs are candidates for functional analyses of genes that affect flower bud development in Fritillaria, and may aid in revealing the molecular mechanism mediating flower bud development in other perennial bulbous plants.