IDENTIFICATION AND CHARACTERIZATION OF DOSOC1 AND DOGAI FROM DENDROBIUM CHAO PRAYA SMILE

Abstract

Orchids are one of the most popular cut-flowers and potted-plants in the world. Hence, it is economically important to generate novel orchid varieties with improved characteristics. As traditional orchid breeding methods are time-consuming, genetic transformation using the characterized genes has been applied to manipulate specific traits of orchids. To facilitate genetic engineering of orchids, we have characterized orchid genes involved in key developmental processes.

In this thesis, we report two genes, DOSOC1 and DOGAI, which are involved in the control of flowering time and the phytohormone gibberellin (GA) signaling in the orchid Dendrobium Chao Praya Smile, respectively. DOSOC1 encodes a MADS-box protein orthologous to SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) in the model plant Arabidopsis. DOSOC1 was highly expressed in reproductive organs, including inflorescence apices, pedicels, floral buds, and open flowers. Overexpression of DOSOC1 resulted in early flowering in wild-type Arabidopsis plants and partially complemented the late-flowering phenotype of Arabidopsis soc1-2 loss-of-function mutants. Furthermore, we successfully created several 35S:DOSOC1 transgenic Dendrobium orchid lines, which consistently exhibited earlier flowering than wild-type orchids.

DOGAI encodes a DELLA protein that acts as a negative regulator in the GA signaling pathway. DOGAI was ubiquitously expressed in orchid tissues. Overexpression of DOGAI in Arabidopsis and Dendrobium orchids displayed GA-deficient phenotypes, including dark-green leaves and dwarf stature. In addition, the GFP-DOGAI fusion protein was degraded rapidly by GA treatment. These results suggest that SOC1-like genes and DELLA-like genes play evolutionarily conserved roles in controlling flowering time and GA signaling in orchids, respectively.