National Research Institute of Brewing, 3-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan
National Research Institute of Brewing, 3-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan.
J Exp Bot. 2014 Aug;65(15):4433-49. doi: 10.1093/jxb/eru213. Epub 2014 May 23.
A new regulator of proanthocyanidin (PA) biosynthesis in grapes was found by screening genes coordinately expressed with PA accumulation under different light conditions using a substantially improved method of serial analysis of gene expression (SuperSAGE). This R2R3-MYB transcription factor, VvMYBPAR, shows high protein sequence similarity with PA biosynthesis-regulating plant MYBs, such as VvMYBPA2 and TRANSPARENT TESTA2. Its transcript levels were relatively high in the skins of young berries, whereas the levels were higher in the seeds and at a maximum around veraison. In addition to its response to modified light conditions, the gene responded to abscisic acid application in the skins of cultured berries. Among the PA-specific branch genes, this transcript profile was not correlated with that of VvANR and VvLAR1 but was closely related to that of VvLAR2, suggesting different regulation of PA-specific branch genes from that of a known PA regulator, VvMYBPA2. The PA-specific regulation of VvMYBPAR was confirmed by VvMYBPAR constitutive expression in Arabidopsis in which the transgene specifically induced PA biosynthetic genes and resulted in PA accumulation in plants grown on sucrose-supplemented media to induce anthocyanin synthesis. A transient reporter assay using grapevine cells showed that VvMYBPAR activated the promoters on PA-specific branch genes and candidate genes associated with modification and transport of monomeric PA precursors, as well as the promoters of VvCHS3 and VvF3'5'Hd in the common flavonoid pathway, but not that of VvUFGT on the anthocyanin-specific branch. This new factor suggests the polygenic regulation of PA biosynthesis in grapes by closely related MYB transcription factors.
利用改良的基因表达系列分析（SuperSAGE）技术，根据不同光条件下与原花青素（PA）积累协同表达的基因筛选出葡萄中 PA 生物合成的新调控因子。该 R2R3-MYB 转录因子 VvMYBPAR 与调节植物 PA 生物合成的 MYB，如 VvMYBPA2 和 TRANSPARENT TESTA2，具有较高的蛋白质序列相似性。其转录本水平在幼果果皮中相对较高，而在种子中较高，并在转色期达到最大值。除了对光照条件的响应外，该基因还对培养浆果果皮中的脱落酸处理有响应。在 PA 特异性分支基因中，该转录谱与 VvANR 和 VvLAR1 无关，但与 VvLAR2 密切相关，表明 PA 特异性分支基因的调控不同于已知的 PA 调控因子 VvMYBPA2。VvMYBPAR 在拟南芥中的组成型表达证实了其对 PA 的特异性调控，该转基因植物特异性诱导 PA 生物合成基因的表达，导致在蔗糖补充培养基上生长的植物中 PA 积累，从而诱导花青素的合成。利用葡萄细胞进行的瞬时报告基因分析表明，VvMYBPAR 激活了 PA 特异性分支基因和与单体 PA 前体修饰和运输相关的候选基因的启动子，以及常见类黄酮途径中 VvCHS3 和 VvF3'5'Hd 的启动子，但对花青素特异性分支上的 VvUFGT 启动子没有作用。这个新因子表明葡萄中 PA 生物合成的多基因调控是由密切相关的 MYB 转录因子来实现的。
