Molecular cloning and expression of a 9-cis-epoxy carotenoid dioxygenase gene (NCED) and its relationship to dormancy in Lilium longiflorum and L. formosanum

Individuals in northern populations of Lilium longiflorum in the Ryukyu Archipelago between Japan and Taiwan exhibit deep dormancy which is induced by high temperatures in the Summer, while plants of southern ecotypes and L. formosanum show no dormancy. In higher plants, 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical enzyme for the regulation of abscisic acid (ABA) biosynthesis. The relationships between levels of expression of the LlNCED gene (GenBank Accession No. KC357734) and endogenous ABA levels were examined in 1-year-old seedlings of an L. formosanum population domesticated in Fukuoka (FFU) and in two L. longiflorum populations native to Pitouchiao (LPI), Taiwan, or Kikai Jima (LKI), Japan. The deduced amino acid sequences of the NCED proteins shared high identity with NCED proteins in other monocotyledons, and were closely related to enzymes in other members of the class Liliopsida. A high correlation was observed between levels of LlNCED gene expression and ABA concentration. Seedlings from LKI had the highest level of expression of LlNCED in August, while seedlings from FFU had the lowest level. Higher expression of the LlNCED gene in mid-Summer in the dormant population was related to higher endogenous concentrations of ABA. These results provide evidence that the induction of deep dormancy was initiated by the accumulation of ABA in dormant types of L. longiflorum, which was induced by high Summer temperatures.