Generation of sesame mutant population by mutagenesis and identification of high oleate mutants by GC analysis

Authors: Wang, Ming; Tonnis, Brandon; Li, Xianran; Morris, John - Brad

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2023
Publication Date: 3/13/2023
Citation: Wang, M.L., Tonnis, B.D., Li, X., Morris, J.B. 2023. Generation of sesame mutant population by mutagenesis and identification of high oleate mutants by GC analysis. Plants. 12(6). https://doi.org/10.3390/plants12061294.
DOI: https://doi.org/10.3390/plants12061294

Interpretive Summary: Sesame is one of the oldest oilseed crops with a long history of cultivation (over 3,000 years). Seeds, leaves, and oil from sesame had been utilized and consumed by human being as food, vegetables, and food ingredient for about 6,000 years. Sesame seeds contain 48-55% oil, 20-28% protein, 14-16% sugars, 6-8% fibers, and other nutritional and bioactive compounds with beneficial effects to human health. The beneficial effects to human health from these bioactive compounds include the prevention of degenerative diseases (such as cancer), cardiovascular diseases, atherosclerosis, and the process of aging. Sesame seeds are very nutritious and tasty after roasting, but the fatty acid composition is not ideal compared with other oilseed crops such as peanut and soybean. Seeds from some newly developed peanut and soybean varieties contain over 80% oleic acid which can extend the shelf-life time and benefit to human health. However, sesame seeds only contain about 40% oleic acid. We took two approaches to improve fatty acid composition in sesame. One was to screen the USDA sesame germplasm collection to identify accessions which have natural mutations for high oleic acid. The second was to chemically mutate elite lines to get high oleic acid. We took both approaches sequentially and produced mutant lines with approximately 75% oleic acid. These mutant lines will be very useful for breeders to develop improved sesame varieties and for scientists to use in further genetic studies.

Technical Abstract: The sesame germplasm accession, PI 263470, which has a significantly higher level of oleic acid (54.0%) than the average (39.5%), was identified by screening the entire USDA germplasm collec-tion. The seeds from this accession were planted in a greenhouse. Leaf tissues and seeds were harvested from individual plants. DNA sequencing of the coding region of fatty acid desaturase gene (FAD2) confirmed that this accession contained a natural mutation of G425A corresponding to the deduced amino acid substitution of R142H leading to the high level of oleic acid, but it was a mixed accession with three genotypes (G/G, G/A, and A/A at the position). The genotype with A/A was selected and self-crossed for three generations. The purified seeds were used for EMS-induced mutagenesis to further enhance the level of oleic acid. 635 M2 mutant plants were generated from mutagenesis. Some mutant plants had significant morphological changes including leafy, flat stems, and others. M3 seeds were used for fatty acid composition analysis by gas chromatography (GC). Several mutant lines were identified with high oleic acid (70%). Six M3 mutant lines plus the check were advanced to M7 or M8 generations. Their high oleate traits from M7 or M8 seeds harvested from M6 or M7 plants were further confirmed. The level of oleic acid from one mutant line (M7 915-2) was over 75%. The coding region of FAD2 was sequenced from these six mutants, but no mutation was identified. Additional loci may contribute to the high level of oleic acid. The mutants identified in this study can be used as breeding materials for sesame improvement and as genetic materials for forward genetic studies.