Exploring Flowering Genes in Phalaenopsis through Transcriptome Analysis and Critical Gene Validation of Hormone Signal Transduction Pathway

In order to study the molecular regulation mechanism of floral transition in Phalaenopsis (Orchidaceae), especially in the hormone signal transduction pathway, the transcriptome of 5 flower developing stages in Phalaenopsis was sequenced, yielding 63 368 unigenes, including 28 339 differentially expressed genes (DEGs). In result, flowering genes were identified, including flower organ identity genes, floral integrator pathway genes, floral meristem identity genes, vernalization pathway genes, age pathway gene, gibberellin (GA) pathway genes, autonomous pathway genes and photoperiod pathway genes. The key genes in plant hormone signal transduction were screened and validated by qRT-PCR. Those genes, including AP1, PIF4X, FT, and TAA2, were highly expressed in the flower bud during the flower initiation and differentiation phases, while GA2ox and PIF4 had lower expression in the flower bud but high expression in the root. The expression of DELLA was up-regulated in the flower bud and down-regulated in the roots; by contrast, the expression of GA2ox was down-regulated in the flower bud and up-regulated in the roots. PIF4 gene expression was remarkably up-regulated in flower stalk, leaves, and roots after spray treatment with GA3 (8.66 × 10–4 mol/L), indicating that PIF4 may be a key gene that directly responds to gibberellin to promote flower initiation.