College of Life Science, Sichuan Agricultural University, No. 46, Xinkang Road, Ya'an, 625014, Sichuan, China.
Department of Biological Science, College of Life Sciences, Sichuan Normal University, Chengdu, 610101, Sichuan, China.
Plant Mol Biol. 2020 Oct;104(3):309-325. doi: 10.1007/s11103-020-01044-5. Epub 2020 Aug 24.
FtMYB18 plays a role in the repression of anthocyanins and proanthocyanidins accumulation by strongly down-regulating the CHS and DFR genes in Tartary buckwheat, and the C5 motif plays an important role in this process. Anthocyanins and proanthocyanidins (PAs) are important flavonoids in Tartary buckwheat (Fagopyrum tataricum Gaertn.), which provides various vibrant color and stronge abiotic stress resistance. Their synthesis is generally regulated by MYB transcription factors at transcription level. However, the negative regulations of MYB and their effects on flavonol metabolism are poorly understood. A SG4-like MYB subfamily TF, FtMYB18, containing C5 motif was identified from Tartary buckwheat. The expression of FtMYB18 was not only showed a negative correlation with anthocyanins and PAs content but also strongly respond to MeJA and ABA. As far as the transgenic lines with FtMYB18 overexpression, anthocyanins and PAs accumulations were decreased through down-regulating expression levels of NtCHS and NtDFR in tobacco, AtDFR and AtTT12 in Arabidopsis, FtCHS, FtDFR and FtANS in Tartary buckwheat hairy roots, respectively. However, FtMYB18 showed no effect on the FLS gene expression and the metabolites content in flavonol synthesis branch. The further molecular interaction analysis indicated FtMYB18 could mediate the inhibition of anthocyanins and PAs synthesis by forming MBW transcriptional complex with FtTT8 and FtTTG1, or MYB-JAZ complex with FtJAZ1/-3/-4/-7. Importantly, in FtMYB18 mutant lines with C5 motif deletion (FtMYB18-C), both of anthocyanins and PAs accumulations had recovered to the similar level as that in wild type, which was attributed to the weakened MBW complex activity or the deficient molecular interaction between FtMYB18ΔC5 with FtJAZ3/-4. The results showed that FtMYB18 could suppress anthocyanins and PAs synthesis at transcription level through the specific interaction of C5 motif with other proteins in Tartary buckwheat.
FtMYB18 通过强烈下调 Tartary 荞麦中的 CHS 和 DFR 基因来抑制花色苷和原花青素的积累，C5 基序在此过程中起重要作用。花色苷和原花青素（PAs）是 Tartary 荞麦（Fagopyrum tataricum Gaertn.）中的重要类黄酮，赋予其各种鲜艳的颜色和较强的非生物胁迫抗性。它们的合成通常在转录水平上受到 MYB 转录因子的调节。然而，MYB 的负调控及其对类黄酮醇代谢的影响知之甚少。从 Tartary 荞麦中鉴定出一个含有 C5 基序的 SG4 样 MYB 亚家族 TF，FtMYB18。FtMYB18 的表达不仅与花色苷和 PAs 含量呈负相关，而且对 MeJA 和 ABA 反应强烈。在过表达 FtMYB18 的转基因烟草、拟南芥中，通过下调 NtCHS 和 NtDFR、AtDFR 和 AtTT12、FtCHS、FtDFR 和 FtANS 的表达水平，花色苷和 PAs 的积累减少。然而，FtMYB18 对 FLS 基因表达和类黄酮醇合成分支代谢物含量没有影响。进一步的分子相互作用分析表明，FtMYB18 可以通过与 FtTT8 和 FtTTG1 形成 MBW 转录复合物，或与 FtJAZ1/-3/-4/-7 形成 MYB-JAZ 复合物，来介导花色苷和 PAs 合成的抑制。重要的是，在 C5 基序缺失（FtMYB18-C）的 FtMYB18 突变体中，花色苷和 PAs 的积累都恢复到与野生型相似的水平，这归因于 MBW 复合物活性减弱或 FtMYB18ΔC5 与 FtJAZ3/-4 之间的分子相互作用缺陷。结果表明，FtMYB18 可以通过 C5 基序与 Tartary 荞麦中其他蛋白质的特异性相互作用，在转录水平上抑制花色苷和 PAs 的合成。
