Espley Richard V, Hellens Roger P, Putterill Jo, Stevenson David E, Kutty-Amma Sumathi, Allan Andrew C
HortResearch, Mt Albert Research Centre, Private Bag 92169, Auckland, New Zealand.
Plant J. 2007 Feb;49(3):414-27. doi: 10.1111/j.1365-313X.2006.02964.x. Epub 2006 Dec 20.
Anthocyanin concentration is an important determinant of the colour of many fruits. In apple (Malus x domestica), centuries of breeding have produced numerous varieties in which levels of anthocyanin pigment vary widely and change in response to environmental and developmental stimuli. The apple fruit cortex is usually colourless, although germplasm does exist where the cortex is highly pigmented due to the accumulation of either anthocyanins or carotenoids. From studies in a diverse array of plant species, it is apparent that anthocyanin biosynthesis is controlled at the level of transcription. Here we report the transcript levels of the anthocyanin biosynthetic genes in a red-fleshed apple compared with a white-fleshed cultivar. We also describe an apple MYB transcription factor, MdMYB10, that is similar in sequence to known anthocyanin regulators in other species. We further show that this transcription factor can induce anthocyanin accumulation in both heterologous and homologous systems, generating pigmented patches in transient assays in tobacco leaves and highly pigmented apple plants following stable transformation with constitutively expressed MdMYB10. Efficient induction of anthocyanin biosynthesis in transient assays by MdMYB10 was dependent on the co-expression of two distinct bHLH proteins from apple, MdbHLH3 and MdbHLH33. The strong correlation between the expression of MdMYB10 and apple anthocyanin levels during fruit development suggests that this transcription factor is responsible for controlling anthocyanin biosynthesis in apple fruit; in the red-fleshed cultivar and in the skin of other varieties, there is an induction of MdMYB10 expression concurrent with colour formation during development. Characterization of MdMYB10 has implications for the development of new varieties through classical breeding or a biotechnological approach.
花青素浓度是许多水果颜色的重要决定因素。在苹果（Malus x domestica）中，经过数百年的培育产生了众多品种，其中花青素色素的含量差异很大，并会随着环境和发育刺激而变化。苹果果实的皮层通常是无色的，不过确实存在一些种质，其皮层由于花青素或类胡萝卜素的积累而具有高度色素沉着。从对多种植物物种的研究来看，很明显花青素生物合成是在转录水平上受到控制的。在此我们报告了红肉苹果与白肉品种相比花青素生物合成基因的转录水平。我们还描述了一种苹果MYB转录因子MdMYB10，其序列与其他物种中已知的花青素调节因子相似。我们进一步表明，这种转录因子能够在异源和同源系统中诱导花青素积累，在用组成型表达的MdMYB10进行稳定转化后，在烟草叶片的瞬时试验中产生色素沉着斑块，以及在苹果植株中产生高度色素沉着。MdMYB10在瞬时试验中对花青素生物合成的有效诱导依赖于苹果中两种不同的bHLH蛋白MdbHLH3和MdbHLH33的共表达。在果实发育过程中，MdMYB10的表达与苹果花青素水平之间的强相关性表明，这种转录因子负责控制苹果果实中的花青素生物合成；在红肉品种和其他品种的果皮中，在发育过程中颜色形成的同时会诱导MdMYB10的表达。对MdMYB10的特性描述对于通过传统育种或生物技术方法培育新品种具有重要意义。
