Characterization of a CONSTANS-like gene from pigeon orchid (Dendrobium crumenatum Swartz) and its Expression under different photoperiod conditions

Abstract

Orchids are economically valuable as cut flowers and in pot plant markets. However, a juvenility phase that is too long is the main disadvantage for commercial orchids. To understand the gene involving floral transition controls in orchids, a CONSTANS-like (COL) gene in the photoperiodic flowering pathway was isolated from Dendrobium crumenatum (pigeon orchid). The cDNA isolated has an open reading frame (ORF) of 969 bp, encoding 322 amino acids. Sequence alignment based on amino acid sequences revealed that the Dendrobium crumenatum COL (DcCOL) shared a high identity with COL isolated from other plant species including Phalaenopsis COL (85%), Oryza sativa Hd1 (70%), Erycina pusilla COL5 (EpCOL5) (66%), and Arabidopsis thaliana CO (39%). DcCOL has three conserved domains (CCT, B-box I, and B-box II domains) and is classified in group I CO/COL by phylogenetic analysis in the Arabidopsis B-box zinc finger protein family. Quantitative real-time RT-PCR demonstrated DcCOL was expressed in all stages of development and all tissue types with the highest expression in floral buds and opened flowers of mature orchids. The expression pattern under photoperiod pathway demonstrated a diurnal expression. The DcCOL was accumulated in the dark in all photoperiodic conditions, i.e., long, neutral, and short days suggesting that the regulation of DcCOL was controlled in a circadian rhythm-dependent manner. The results suggested that photoperiodism is not the main factor in D. crumenatum floral induction control. This DcCOL expression pattern coincided with the D. crumenatum flowering behavior in which the flowering occurs before dawn and lasts for only 24 h implying the function of DcCOL is related to flowering.