The plant-specific transcription factor, LEAFY (LFY) is considered to be a master regulator of flower development in the model plant, Arabidopsis. This protein plays a dual role in plant growth, integrating signals from the floral inductive pathways and acting as a floral meristem identity gene by activating genes for floral organ development. Although LFY occupies an important position in flower development, the functional divergence of LFY homologues has been demonstrated in several plants including monocots and gymnosperms. In particular, the functional roles of LFY genes from orchid species such as Phalaenopsis that contain unique floral morphologies with distinct expression patterns of floral organ identity genes remain elusive. Here, PaLFY, a orthologue of Arabidopsis LFY from Phalaenopsis aphrodite subsp. formosana, a Taiwanese native monopodial orchid was isolated and characterized through analyses of expression and protein activity. PaLFY transcripts accumulated in the floral primordia of developing inflorescences and the PaLFY protein had transcriptional autoactivation activity forming as a homodimer. Furthermore, PaLFY rescues the aberrant floral phenotypes of Arabidopsis lfy mutants. Over-expression of PaLFY alone or together with PaFT1, a P. aphrodite subsp. formosana homologue of Arabidopsis FLOWERING LOCUS T (FT) in rice caused precocious heading. Consistently, higher chlorophyll content in the sepals and morphological changes in epidermal cells were observed in the floral organs of PaLFY knock-down orchids generated by virus-induced gene silencing. Taken together, these results suggest that PaLFY is functionally distinct from RICE FLORICAULA/LEAFY (RFL) but similar to Arabidopsis LFY based on phenotypes of our transgenic Arabidopsis and rice plants.

• Seonghoe Jang(Biotechnology Center in Southern Taiwan/Agricultural Biotechnology Research Center, Academia Sinica, Taiwan, Institute of Tropical Plant Science, National Cheng Kung University, Taiwan)