The genus Brassica encompasses crops such as broccoli, brussel sprouts, cabbage and cauliflower. In addition turnips and choy sum, an Asian vegetable, belong to the Brassica genus. Finally mustards, canola or rapeseed and rutabaga are species of Brassica as well.
The patents granted to Calgene in the United States and in Europe are directed to transgenic Brassica cells containing expression cassettes inserted in their genome through co-cultivation with a disarmed Agrobacterium tumefaciens. Brassica explants, such as leaf and hypocotyl tissue, and protocols to achieve transformation are claimed as well as the component elements of the expression cassettes.
One the most limiting aspects of the claimed inventions is the sequences of the expression cassette or construct inserted into the genome of Brassica plants. In this regard the expression cassette must contain the following elements in 5' to 3' order:
- a transcription initiation region;
- an open reading frame (ORF) or a sequence complementary to an endogenous sequence of a plant;
- a right T-DNA border; and
- a structural gene.
AgrEvo (now Bayer Crop Science) has a granted United States patent that is directed to a method to produce a transgenic Brassica microspore using Agrobacterium . The microspore is treated first with a mucolytic enzyme to kill the bacteria and then develops into a haploid or doubled haploid embryo and ultimately a homozygous transgenic plant (Update July 2003).
The University of Helsinki has granted Australian and United States patents and a European application directed to the transformation of turnip rape (Brassica rapa ) with A. tumefaciens. The claims as granted in Australia and in the US and claims as filed in Europe are fairly narrow in scope; the methods comprise very detailed steps, e.g. type of tissue to be transformed and specific, pre-cultivation and co-cultivation conditions.
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