Plant regeneration and Agrobacterium-mediated genetic transformation systems in liliaceous ornamental plants

The family Liliaceae (Cronquist system) contains various important ornamental plants. We have been examining for about 20 years the establishment of plant regeneration and genetic transformation systems in liliaceous ornamental plants for their biotechnological breeding and elucidation of the molecular mechanisms determining ornamental traits. In this review, studies on in vitro plant regeneration in 7 genera and on Agrobacterium-mediated production of transgenic plants in 4 genera are described. Plant regeneration was achieved via callus cultures in Agapanthus, Hemerocallis, Hosta, Lilium, Muscari and Tricyrtis. Auxins (2,4-dichrolophenoxyacetic acid, α-naphthaleneacetic acid and/or picloram) were effective for inducing regenerable calli. Tulipa species and cultivars were very recalcitrant to callus induction and plant regeneration. Agrobacterium-mediated transformation was examined in Agapanthus, Lilium, Muscari and Tricyrtis, and transgenic plants were obtained in all genera by using regenerable calli as a target material for Agrobacterium inoculation, inoculation and co-cultivation with Agrobacterium in the presence of acetosyringone, and selection of transgenic tissues and plantlets on hygromycin-containing media. Among 4 genera, Tricyrtis has several advantages for transformation studies: higher transformation efficiency, relatively small plant size, ease of cultivation, and taking only 1 year from in vitro regeneration to flowering. We are now investigating the molecular mechanisms for determining plant form, flower color and flower form by using Tricyrtis spp. as liliaceous model plants.