Induced mutagenesis in UGT74S1 gene leads to stable new flax lines with altered secoisolariciresinol diglucoside (SDG) profiles
Fofana, B., Ghose, K., Somalraju, A., McCallum, J., Main, D., Deyholos, M.K., Rowland, G.G., Cloutier, S. (2017). Induced mutagenesis in UGT74S1 gene leads to stable new flax lines with altered secoisolariciresinol diglucoside (SDG) profiles. Frontiers in Plant Science, [online] 8 http://dx.doi.org/10.3389/fpls.2017.01638
Plain language summary
In this study, researchers hypothesized that the flax gene, UGT74S1, may be the unique player for decorating the backbone molecule of the flax lignan by adding two sugars to form the final lignan compound. To verify this hypothesis, the authors adopted a mutation genetics approach by using a chemical that can modify the structure and function of genes in a large population of flax plants. Then, they monitored the changes in the gene structure and the profiles of its end products in the seed collected from individual flax plants. The results showed that the chemical induced stable mutations in the flax lines after several self-pollinations. The study further demonstrated that the gene under study is not only unique in performing this biochemical process, but also showed that changes at specific locations of the gene lead to a new compound not naturally found in the flax seed; and this new compound is potentially more bioactive in human chronic diseases than its native form usually observed in flax seed. The study is first to demonstrate the production of a new lignan compound in flax seed without using a transgenic approach. The data also showed that the chemical induced other changes in flax genetic make-up and caused a wide diversity of the naturally-occurring lignan's content in the population. Altogether, the created mutant flax lines constitute a non-GMO genetic resource for flax breeders and the UGT74S1 gene can be used for engineering flax lignan compounds in vitro by fermentation in a yeast system.
Flax secoisolariciresinol (SECO) diglucoside (SDG) lignan is an emerging natural product purported to prevent chronic diseases in humans. SECO, the aglycone form of SDG, has shown higher intestinal cell absorption but it is not accumulated naturally in planta. Recently, we have identified and characterized a UDP-glucosyltransferase gene, UGT74S1, that glucosylates SECO into its monoglucoside (SMG) and SDG forms when expressed in yeast. However, whether this gene is unique in controlling SECO glucosylation into SDG in planta is unclear. Here, we report on the use of UGT74S1 in reverse and forward genetics to characterize an ethyl methane sulfonate (EMS) mutagenized flax population from cultivar CDC Bethune and consisting of 1996 M2 families. EMS mutagenesis generated 73 SNP variants causing 79 mutational events in the UGT74S1 exonic regions of 93 M2 families. The mutation frequency in the exonic regions was determined to be one per 28 Kb. Of these mutations, 13 homozygous missense mutations and two homozygous nonsense mutations were observed and all were transmitted into the M3 and M4 generations. Forward genetics screening of the population showed homozygous nonsense mutants completely lacking SDG biosynthesis while the production of SMG was observed only in a subset of the M4 lines. Heterozygous or homozygous M4 missense mutants displayed a wide range of SDG levels, some being greater than those of CDC Bethune. No additional deleterious mutations were detected in these mutant lines using a panel of 10 other genes potentially involved in the lignan biosynthesis. This study provides further evidence that UGT74S1 is unique in controlling SDG formation from SECO and this is the first report of non-transgenic flax germplasm with simultaneous knockout of SDG and presence of SMG in planta.