Prolonging the longevity of cymbidium flowers through genetic transformation

A substantial portion of commercially produced cymbidiums is sold as cut flowers that often require shipment to distant markets. Like many other species, ethylene released following harvest causes short flower longevity. The loss of flowers might be minimized by genetically transforming plants for reduced sensitivity to ethylene. A Cymbidium hybrid that produces large, dark pink-reddish flowers was selected for transformation. Shoot tips were excised and cultured in vitro, and protocorms were bombarded with a plasmid construct containing the boers gene, a mutant of the ethylene receptor gene, ERS, isolated from Brassica oleracea var. botrytis L. The mutant confers reduced sensitivity to ethylene. The ubiquitin promoter together with the hygromycin resistance gene was included in the construct. Bombardment was performed with the BioRad Biolistic PDS-1000/He gun. After 80 days of culture on hygromycin containing medium, putative transformants were isolated as regenerating protocorms. Protocorms also gave rise to plant differentiation subsequently in hygromycin containing culture medium. Transformants were preliminarily confirmed by PCR and RT-PCR for HPH and boers genes, and ultimately verified by genomic Southern hybridization. GC analysis of volatiles collected from leaves of transformed and nontransformed plantlets showed different rates of ethylene evolution. However, exposure of the leaves to exogenous ethylene caused rapid browning of leaves of nontransformed plants, but not of those from transformed plants. At this writing, the transgenic cymbidium plants are continuing to grow vigorously in the greenhouse, but have not yet matured for studying the ethylene sensitivity of their excised or intact flowers.