Biolistic transformation of cotton embryogenic cell suspension cultures

Genetic transformation of cotton (Gossypium hirsutum L.) is highly dependent on the ability to regenerate fertile plants from transgenic cells through somatic embryogenesis. Induction of embryogenic cell cultures is genotype dependant. However, once embryogenic cell cultures are available, they can be effectively used for transformation by Agrobacterium or biolistic bombardment methods. Here I describe a detailed procedure to transform cotton embryogenic cell suspension cultures by biolistic bombardment. A commercially available, helium-driven biolistic device (Bio-Rad PDS1000/He) was used to bombard gold particles coated with plasmid DNA (for visual identification of transformed cells and/or selection) into embryogenic cells. Stable transformation at a high frequency (up to 4% of the transiently expressing cells) is possible. Regeneration of fertile transgenic plants from embryogenic cells takes only about 2 months. Another advantage of the embryogenic cell suspension cultures is that they are amenable for cryopreservation and long-term storage. It is highly preferable to transform commercial varieties of choice than obsolete varieties to avoid the genetic drag due to backcrossing.