National Institute of Agricultural Science, Rural Development Administration , JeonJu 54874, Republic of Korea.
Department of Genetic Engineering and Graduate School of Biotechnology, Kyung Hee University , Yongin 17104, Republic of Korea.
J Agric Food Chem. 2017 Jul 5;65(26):5287-5298. doi: 10.1021/acs.jafc.7b01036. Epub 2017 Jun 23.
We isolated cDNAs encoding flavonol synthase (FLS) from the red onion "H6" (AcFLS-H6) and the yellow onion "Hwangryongball" (AcFLS-HRB). We found three amino acid variations between the two sequences. Kinetic analysis with recombinant proteins revealed that AcFLS-HRB exhibited approximately 2-fold higher catalytic efficiencies than AcFLS-H6 for dihydroflavonol substrates and that both proteins preferred dihydroquercetin to dihydrokaempferol. The expression patterns of flavonoid biosynthesis genes corresponded to the accumulation patterns of flavonoid aglycones in both onions. Whereas the other flavonoid biosynthesis genes were weakly expressed in the HRB sheath compared to that of H6, the expression of FLS was similar in both onions. This relatively enhanced FLS expression, along with the higher activity of AcFLS-HRB, could increase the quercetin production in the HRB sheath. The quercetin content was approximately 12-fold higher than the cyanidin content in the H6 sheath, suggesting that FLS has priority in the competition between FLS and dihydroflavonol 4-reductase (DFR) for their substrate dihydroquercetin.
我们从红洋葱“H6”（AcFLS-H6）和黄洋葱“黄洋葱球”（AcFLS-HRB）中分离出编码类黄酮合酶（FLS）的 cDNA。我们发现这两个序列之间有三个氨基酸差异。用重组蛋白进行的动力学分析表明，AcFLS-HRB 对二氢黄酮醇底物的催化效率比 AcFLS-H6 高约 2 倍，并且两种蛋白质都优先选择二氢槲皮素而不是二氢山奈酚。类黄酮生物合成基因的表达模式与两种洋葱中类黄酮苷元的积累模式相对应。虽然与 H6 相比，其他类黄酮生物合成基因在 HRB 鞘中的表达较弱，但 FLS 在两种洋葱中的表达相似。这种相对增强的 FLS 表达，加上 AcFLS-HRB 的高活性，可能会增加 HRB 鞘中槲皮素的产量。槲皮素的含量大约是 H6 鞘中矢车菊素含量的 12 倍，这表明 FLS 在 FLS 和二氢黄酮醇 4-还原酶（DFR）之间对其底物二氢槲皮素的竞争中具有优先权。
