Enhancement of syringin contents in soybean seeds with seed-specific expression of a chimeric UGT72E3/E2 gene

Syringin, sinapyl alcohol 4- O -glucoside, is well known as a plant-derived bioactive monolignol glucoside. In Arabidopsis , recombinant chimeric protein UGT72E3/2 has been previously reported to lead to significantly higher syringin production than the parental enzymes UGT72E2 and UGT72E3. To enhance syringin content in Korean soybean ( Glycine max L. ‘Kwangan’), we cloned the UGT72E3 / 2 gene under the control of the β-conglycinin or CaMV-35S promoter to generate β -UGT72E3 / 2 and 35S -UGT72E3 / 2 constructs, respectively, and then transformed them into soybean to obtain transgenic plants using the modified half-seed method. Real-time semi-quantitative PCR (RT-PCR) analysis showed that the UGT72E3 / 2 gene was expressed in the leaves of the β -UGT72E3 / 2 and 35S -UGT72E3 / 2 transgenic lines. HPLC analysis of the seeds and mature tissues of the T2 generation plants revealed that the β -UGT72E3 / 2 transgenic seeds accumulated 0.15 µmol/g DW of total syringin and 0.29 µmol/g DW of total coniferin, whereas coniferin and syringin were not detected in non-transgenic seeds. Moreover, coniferin and syringin also accumulated at high levels in non-seed tissues, particularly the leaves of β -UGT72E3 / 2 transgenic lines. In contrast, 35S -UGT72E3 / 2 lines showed no differences in the contents of coniferin and syringin between transgenic and non-transgenic soybean plants. Thus, the seed-specific β-conglycinin promoter might be an effective tool to apply to the nutritional enhancement of soybean crops through increased syringin production.