Genetic engineering of chrysanthemum (Chrysanthemum morifolium) : Current progress and perspectives

We give an overview of the advances of an Agrobacterium-mediated transformation system, clarifying its problems and their solutions, and then show the latest version of our transformation system and examples of the introduction of agronomically important traits into chrysanthemums. Typical problems with the Agrobacterium-mediated transformation in chrysanthemum include low transformation e ciency, high chimerism and cultivar speci city. Using a co-cultivation medium containing acetosyringone and casamino acids for high transformation e ciency and an antibioticselection step for transgenic calli before plant regeneration to eliminate the chimerism, we established an e cient and stable transformation system for chrysanthemum. In addition, this system was used to successfully introduce useful agronomical traits, such as insect resistance and new ower color, into chrysanthemums. ese traits have been stably and highly expressed to confer the expected characteristics upon the transgenic chrysanthemums. Before applying a eld trial of the genetically modi ed (GM) chrysanthemums, male and female sterility were introduced into the transformants to exclude the transgene ow from the GM plants to their wild relatives. So far, using RNAi technology, some of the transgenic chrysanthemums have displayed complete male sterility with very weak female fertility.