Bogs Jochen, Jaffé Felix W, Takos Adam M, Walker Amanda R, Robinson Simon P
Commonwealth Scientific and Industrial Research Organization Plant Industry, Glen Osmond, 5064, Australia.
Plant Physiol. 2007 Mar;143(3):1347-61. doi: 10.1104/pp.106.093203. Epub 2007 Jan 5.
Proanthocyanidins (PAs; or condensed tannins) can protect plants against herbivores, contribute to the taste of many fruits, and act as dietary antioxidants beneficial for human health. We have previously shown that in grapevine (Vitis vinifera) PA synthesis involves both leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR). Here we report the characterization of a grapevine MYB transcription factor VvMYBPA1, which controls expression of PA pathway genes including both LAR and ANR. Expression of VvMYBPA1 in grape berries correlated with PA accumulation during early berry development and in seeds. In a transient assay, VvMYBPA1 activated the promoters of LAR and ANR, as well as the promoters of several of the general flavonoid pathway genes. VvMYBPA1 did not activate the promoter of VvUFGT, which encodes the anthocyanin-specific enzyme UDP-glucose:flavonoid-3-O-glucosyltransferase, suggesting VvMYBPA1 is specific to regulation of PA biosynthesis in grapes. The Arabidopsis (Arabidopsis thaliana) MYB transcription factor TRANSPARENT TESTA2 (TT2) regulates PA synthesis in the seed coat of Arabidopsis. By complementing the PA-deficient seed phenotype of the Arabidopsis tt2 mutant with VvMYBPA1, we confirmed the function of VvMYBPA1 as a transcriptional regulator of PA synthesis. In contrast to ectopic expression of TT2 in Arabidopsis, constitutive expression of VvMYBPA1 resulted in accumulation of PAs in cotyledons, vegetative meristems, leaf hairs, and roots in some of the transgenic seedlings. To our knowledge, this is the first report of a MYB factor that controls genes of the PA pathway in fruit, including both LAR and ANR, and this single MYB factor can induce ectopic PA accumulation in Arabidopsis.
原花青素（PAs；或缩合单宁）可以保护植物免受食草动物侵害，影响许多水果的口感，并作为对人体健康有益的膳食抗氧化剂。我们之前已经表明，在葡萄（葡萄属）中，PA的合成涉及无色花青素还原酶（LAR）和花青素还原酶（ANR）。在此，我们报道了一种葡萄MYB转录因子VvMYBPA1的特性，它控制包括LAR和ANR在内的PA途径基因的表达。VvMYBPA1在葡萄浆果中的表达与浆果早期发育期间以及种子中的PA积累相关。在瞬时试验中，VvMYBPA1激活了LAR和ANR的启动子，以及几个类黄酮通用途径基因的启动子。VvMYBPA1没有激活编码花青素特异性酶UDP-葡萄糖：类黄酮-3-O-葡萄糖基转移酶的VvUFGT的启动子，这表明VvMYBPA1对葡萄中PA生物合成的调控具有特异性。拟南芥的MYB转录因子透明种皮2（TT2）调节拟南芥种皮中的PA合成。通过用VvMYBPA1互补拟南芥tt2突变体的PA缺陷种子表型，我们证实了VvMYBPA1作为PA合成转录调节因子的功能。与TT2在拟南芥中的异位表达不同，VvMYBPA1的组成型表达导致一些转基因幼苗的子叶、营养分生组织、叶毛和根中积累了PA。据我们所知，这是关于控制果实中PA途径基因（包括LAR和ANR）的MYB因子的首次报道，并且这个单一的MYB因子可以在拟南芥中诱导异位PA积累。
