Cibus Canada Inc. has developed a canola event that is tolerant to
the sulfonylurea herbicides tribenuron-methyl and
thifensulfuron-methyl. The development of canola event 5715 was
accomplished by conventional breeding of two herbicide tolerant
mutants, one newly produced and one commercially available. Cibus
Canada Inc. utilized an oligonucleotide-directed mutagenesis
approach known as the Rapid Trait Development System™ (RTDS™),
which included the application of tissue culture techniques that
generated plant cells more receptive to mutagenesis.
Brassica napus (B. napus) carries two complete genomes designated
"A" and "C". Each genome has an acetohydroxyacid synthase (AHAS)
gene (BnAHAS1 gene in the C genome and BnAHAS3 in the A genome)
coding for an AHAS enzyme.
Tolerance to the sulfonylurea herbicides is achieved in canola
event 5715 through the presence of the same single point mutation,
known as the PM2 mutation, in both the BnAHAS1 and BnAHAS3 genes.
This mutation results in modified AHAS enzymes carrying a single
amino acid substitution which renders them insensitive to
tribenuron-methyl and thifensulfuron-methyl.
It should be noted that the PM2 mutation confers tolerance to a
range of AHAS-inhibiting herbicides commonly referred to as the
"group 2" herbicides (i.e. the imidazolinones,
sulfonylureas and triazolopyrimidines).