Optimization of Brassica napus (canola) explant regeneration for genetic transformation

Brassica napus (canola) is the second largest oilseed crop in the world. It is among the first crops to be genetically transformed, and genetically modified cultivars are in commercial production at very significant levels. Despite the early lead with respect to transgenesis, there remain cultivars that are recalcitrant to transformation. To address this, we have conducted an elaborate investigation of the conditions for regenerating shoots from hypocotyl explants from four genetic lines: Invigor 5020, Westar and Topas as well as a microspore culture derived line of Topas (Line 4079). We analyzed the effect of hormonal combinations in regeneration medium, donor plant age and explant type on the regeneration capacity of these plants. The analysis showed that hypocotyls of eight-day-old seedlings grown on media supplemented with 1 mg/L dinitrophenylhydrazine (2,4-D) produced the most shoots. Globular somatic embryos emerged following two weeks of 2,4-D treatment. When transferred to the medium containing 5 mg/L benzyladenine (BA), approximately 82% of embryos produced shoots within six weeks. Invigor plants were shown to regenerate more efficiently than Topas; the number of plantlets regenerated from Invigor was approximately 40–50% more as compared to Topas or Line 4079. When hypocotyl explants were co-cultivated with the Agrobacterium strain GV3101 harboring a binary vector carrying a firefly luciferase reporter gene (LUC), significant numbers of plantlets were LUC-positive in a luciferase assay. Frequency of such plants were: Invigor 5020 (54.2 ± 2.5%), Westar (53.7 ± 5.3), Topas (16.0 ± 0.24) and Line 4079 (13.4 ± 4).