Molecular Cloning and Functional Analysis of Three CONSTANS-Like Genes from Chinese Cymbidium

Abstract

CONSTANS (CO) and CONSTANS-like (COL) are two centrally important flowering-related genes in the photoperiodic pathway of Cymbidium, an economically important orchid genus within the Orchidaceae. To assess how photoperiod affects flowering in three Cymbidium species, CsCOL1, CgCOL, and CeCOL were isolated and characterized from Cymbidium sinense, Cymbidium goeringii, and Cymbidium ensifolium, respectively. CsCOL1, CgCOL, and CeCOL, which contain a CCT domain and two conserved B-box zinc fingers, belong to Group Ic in the CO/COL protein family. These three genes, which were expressed in all organs, especially in the leaves, exhibited the same diurnal rhythm and were abundant in the late light period under long days (LD). However, their diurnal oscillation rhythm under short days (SD) differed. CsCOL1 was highly transcribed in the late dark period under SD. CeCOL was rapidly suppressed in the light, increased in the dark, and peaked at the end of the dark period under SD. CgCOL expression gradually increased, peaking after 4 h of darkness under SD. When CsCOL1 and CeCOL were overexpressed in Arabidopsis under LD, flowering was promoted, suggesting that CsCOL1 and CeCOL may be floral inducers in C. sinense and C. ensifolium, respectively. The overexpression of CgCOL delayed flowering in Arabidopsis, suggesting that it may act as a floral repressor in C. goeringii. This study provides greater insight into the molecular mechanisms regulating flowering time in three Cymbidium species, specifically related to photoperiod. This has practical implications for controlled flower production in potted Cymbidium greenhouse production systems.