Abstract
Phalaenopsis is a winter-blooming orchid genus commonly cultivated in tropical Asian countries. Because orchid is one of the most economically important flower crops in Taiwan, it is crucial to understand its response to cold and other abiotic stresses. The present study focused on gene regulation of P. aphrodite in response to abiotic stress, mainly cold. Our results demonstrate that P. aphrodite is sensitive to low temperatures, especially in its reproductive stage. We found that after exposure to 4°C, plants in the vegetative stage maintained better membrane integrity and photosynthetic capacity than in the flowering stage. At the molecular level, C-repeat binding factor1 (PaCBF1) and its putative target gene dehydrin1 (PaDHN1) mRNAs were induced by cold, whereas inducer of CBF expression1 (PaICE1) mRNAs were constitutively expressed. PaICE1 transactivated MYC motifs in the PaCBF1 promoter, indicating that up-regulation of PaCBF1 may be mediated by the binding of PaICE1 to MYC motifs. PaCBF1 transactivated PaDHN1 at cold treatment, suggesting PaCBF1 was involved in the cold-regulation of PaDHN1. Overexpression of PaCBF1 in transgenic Arabidopsis induced AtCOR6.6 and RD29a without cold stimulus and maintain better membrane integrity after cold stress. Herein, we present evidence that cold induction of PaCBF1 transcripts in P. aphrodite may be transactivated by PaICE1 and consequently protect plants from cold damage through up-regulation of cold-regulated (COR) genes, such as DHN. To our knowledge, this study is the first report of isolation and characterization of CBF, DHN and ICE genes in the Orchidaceae family.