Abstract

Sesame (Sesamum indicum L.) seed is source of high quality edible oil for which the market niche can be expanded by developing cultivars with altered fatty acid composition through conventional breeding or genetic transformation. There is need to know the natural diversity in oil quality to facilitate breeding, while reliable regeneration and transformation protocols need to be developed for genetic engineering. The seed oil diversity in thirty sesame accessions from East Africa over three years, and the regeneration and floral transformation potential of selected accessions were studied. The effectiveness of a cloned sesame oleate desaturase was tested in Arabidopsis thaliana. Significant variation was observed among the accessions for the oil content and the quantity of individual fatty acids in each of the three years of field evaluation. There was positive correlation between oil content and stearic and oleic acid levels. Shoot regeneration was achieved from cotyledon explants, whereas hypocotyl explants only gave callus and roots. Some accessions were more amenable to regeneration than others. A high rate of sesame transformation using Agrobacterium tumefaciens carrying a binary vector containing the neomycin phosphotransferase (NPT) II gene for kanamycin resistance and the enhanced green fluorescent protein (EGFP) reporter gene was achieved through floral dipping, pollen infiltration and suspension drop. Pollen infiltration and suspension drop produced higher transformation frequencies than floral dip. Agrobacterium strains EHA 105 and GV3101 gave higher transformation than GV2260. The best sesame cultivars for transformation were Mtwara-2 and McBlack. A Δ12 oleate desaturase cDNA isolated from immature seeds had its function confirmed by its complementation of the fad2-2 mutant phenotype of A. thaliana. The cDNA was also expressed in transgenic A. thaliana lines that synthesize epoxy, hydroxy and acetylenic fatty acids, and shown to influence the accumulation of linoleic and the unusual fatty acids. The major contribution of this study is the development of novel regeneration and transformation techniques for sesame, which open new avenues for the genetic improvement of the crop.