Objective Major endogenous hormones in flower bud and leaf bud oncidium were analyzed to study the flowering regulation mechanism for commercial cutting and potting control of the ornamental plant.

Methods Contents of IAA, TZR, ABA, and GA₃ in leaves and pseudobulbs of oncidium flower and leaf bud plants were analyzed. Key differentially expressed genes (DEGs) in the hormone signal transduction pathways were identified by transcriptome sequencing (RNA-seq).

Results (1) On a flower bud plant, IAA, TZR, ABA, and GA₃ in the leaves significantly increased over those on the leaf bud plants; so did TZR and ABA in the pseudobulbs, while IAA and GA₃ declined. In the leaves of flower bud plants, the ratios of IAA/TZR, IAA/ABA, IAA/GA₃, and TZR/ABA decreased, but TZR/GA₃ and ABA/GA₃ rose. In the pseudobulbs, on the other hand, IAA/TZR and IAA/ABA ratios were lower and IAA/GA₃, TZR/GA₃, and ABA/GA₃ became higher. (2) There were 2 439 up-regulated and 3 108 down-regulated totaling 5 547 DEGs in the leaves; and in the pseudobulbs, 1 600 up-regulated and 1 208 down-regulated. The DEGs-enriched KEGG pathways were associated with biosynthesis of secondary metabolites, carotenoid, zeatin, and diterpeneoid. Eight of the 86 DEGs in the plant hormone signal transduction pathway, i.e., ARF, AHP, A-ARR, DELLA, PIF, PYR/PYL, etc., were significantly differentiated in the leaves as well as the pseudobulbs.

Conclusion The differentiated phytohormones in leaves and pseudobulbs as well as the DEGs related to plant hormone signal transduction during the morphological differentiation of flower buds and leaf buds on an oncidium plant were analyzed. Elevated TZR and ABA, high TZR/GA₃ and ABA/GA₃ as well as low IAA/TZR and IAA/ABA were postulated to stimulate the flower bud differentiation. And ARF, AHP, and PIF were the pivotal genes associated with the flowering regulation mechanism.