The cowpea event 245F was produced by Agrobacterium tumefaciens-mediated transformation with plasmid pMB6. The event contains two gene cassettes:

• The first cassette contains the Cry2Ab encoding gene from Bacillus thuringiensis subs. kurstaki strain HD-1. The nucleotide sequence of the cry2Ab gene was codon-optimized for plant expression and includes one extra amino acid near the N-terminus, aspartic acid, which was introduced during cloning. The Cry2Ab protein confers resistance to the pod borer, Maruca vitrata.

• The second cassette contains a copy of the nptII encoding gene from the Tn5 transposon of Escherichia coli strain K12. To eliminate leaky expression of NPTII in Agrobacterium and prevent selection of false-positive kanamycin-resistant plants, the nptII gene was interrupted with a modified catalase-1 (CAT-1) intron from castor bean (Riccinus communis) (Ohta et al., 1990; Schünmann et al., 2003b). Transcription of the nptII gene is controlled by the S1 promoter from Subterranean clover stunt virus (SCSV) and termination sequences are provided by the SCSV DNA segment 3.

Pod borer resistant cowpea with event 245F will not be commercialized as a stand-alone product but will be combined with other cowpea varieties containing event 709A using conventional and molecular breeding. This will produce new varieties containing Cry1Ab proteins, derived from event 709A, and the Cry2Ab protein, derived from event 245F cowpea. The new cowpea varieties carrying more than one protective gene will deliver durable resistance and offer a sustainable solution to the damage caused by M. vitrata.

Molecular characterization of 245F cowpea confirmed the presence of the T-DNA region derived from plasmid pMB6 at a single insertion site that was stably inherited over multiple generations as a single genetic locus.

Source: NBMA Nigeria.