UGT74S1 is the key player in controlling secoisolariciresinol diglucoside (SDG) formation in flax.
Flax lignan, commonly known as secoisolariciresinol (SECO) diglucoside (SDG), has recently been reported with health-promoting activities, including its positive impact in metabolic diseases. However, not much was reported on the biosynthesis of SDG and its monoglucoside (SMG) until lately. Flax UGT74S1 was recently reported to sequentially glucosylate SECO into SMG and SDG in vitro. However, whether this gene is the only UGT achieving SECO glucosylation in flax was not known.



Flax genome-wide mining for UGTs was performed. Phylogenetic and gene duplication analyses, heterologous gene expression and enzyme assays were conducted to identify family members closely related to UGT74S1 and to establish their roles in SECO glucosylation. A total of 299 different UGTs were identified, of which 241 (81%) were duplicated. Flax UGTs diverged 2.4-153.6 MYA and 71% were found to be under purifying selection pressure. UGT74S1, a single copy gene located on chromosome 7, displayed no evidence of duplication and was deemed to be under positive selection pressure. The phylogenetic analysis identified four main clusters where cluster 4, which included UGT74S1, was the most diverse. The duplicated UGT74S4 and UGT74S3, located on chromosomes 8 and 14, respectively, were the most closely related to UGT74S1 and were differentially expressed in different tissues. Heterologous expression levels of UGT74S1, UGT74S4 and UGT74S3 proteins were similar but UGT74S4 and UGT74S3 glucosylation activity towards SECO was seven fold less than UGT74S1. In addition, they both failed to produce SDG, suggesting neofunctionalization following their divergence from UGT74S1.



We showed that UGT74S1 is closely related to two duplicated genes, UGT74S4 and UGT74S3 which, unlike UGT74S1, failed to glucosylate SMG into SDG. The study suggests that UGT74S1 may be the key player in controlling SECO glucosylation into SDG in flax although its closely related genes may also contribute to a minor extent in supplying the SMG precursor to UGT74S1.
Charlottetown Research and Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, Prince Edward Island, C1A 4N6, Canada. bourlaye.fofana@agr.gc.ca.
Bourlaye
B
Fofana
Charlottetown Research and Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, Prince Edward Island, C1A 4N6, Canada.|Department of Plant and Soil Science, Texas Tech University, Lubbock, TX, 79409, USA.
Kaushik
K
Ghose
Charlottetown Research and Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, Prince Edward Island, C1A 4N6, Canada.
Jason
J
McCallum
Morden Research and Development Centre, Agriculture and Agri-Food Canada, 101 Route 100 Unit 100, Morden, Manitoba, R6M 1Y5, Canada.
Frank M
FM
You
Ottawa Research and Development Centre, Agriculture and Agri-Food Canada, 960 Carling Avenue, Ottawa, Ontario, K1A 0C6, Canada.
Sylvie
S
Cloutier
D002072:Butylene Glycols / Q000378:metabolism*; D019143:Evolution, Molecular; D019597:Flax / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D020440:Gene Duplication; D015870:Gene Expression; D017343:Genes, Plant; D014644:Genetic Variation; D018745:Genome, Plant; D005960:Glucosides / Q000378:metabolism*; D017705:Lignans / Q000378:metabolism*
D002072:Butylene Glycols; D005960:Glucosides; D017705:Lignans; C060283:secoisolariciresinol; C090142:secoisolariciresinol diglucoside
Flax; Gene duplication; Genome mining; Neofunctionalization; SDG lignan; Secoisolariciresinol; UGTs