Dietary anthocyanins are important health-promoting antioxidants that make a major contribution to the quality of fruits. It is intriguing that most tomato cultivars do not produce anthocyanins in fruit. However, the purple tomato variety Indigo Rose, which has the dominant Aft locus combined with the recessive atv locus from wild tomato species, exhibits light-dependent anthocyanin accumulation in the fruit skin. Here, we report that Aft encodes a functional anthocyanin activator named SlAN2-like, while atv encodes a nonfunctional version of the anthocyanin repressor SlMYBATV. The expression of SlAN2-like is responsive to light, and the functional SlAN2-like can activate the expression of both anthocyanin biosynthetic genes and their regulatory genes, suggesting that SlAN2-like acts as a master regulator in the activation of anthocyanin biosynthesis. We further showed that cultivated tomatoes contain nonfunctional alleles of SlAN2-like and therefore fail to produce anthocyanins. Consistently, expression of a functional SlAN2-like gene driven by the fruit-specific promoter in a tomato cultivar led to the activation of the entire anthocyanin biosynthesis pathway and high-level accumulation of anthocyanins in both the peel and flesh. Taken together, our study exemplifies that efficient engineering of complex metabolic pathways could be achieved through tissue-specific expression of master transcriptional regulators.

饮食中的花色苷是重要的促进健康的抗氧化剂，对水果的品质做出了重要贡献。有趣的是，大多数番茄品种不会在果实中产生花青素。但是，紫色番茄品种Indigo Rose具有主要的Aft基因座与野生番茄物种的隐性atv基因座，在果皮中显示出光依赖性的花青素积聚。在这里，我们报告说，Aft编码一个功能性花青素激活剂，称为SlAN2-like，而atv编码一个非功能性版本的花青素阻遏物SlMYBATV。类SlaN2的表达它对光有反应，功能性的SlaN2-like可以激活花青素生物合成基因及其调节基因的表达，这表明SlaN2-like在花青素生物合成的激活中起主要调节剂的作用。我们进一步表明，栽培番茄含有类似SlAN2的非功能性等位基因， 因此无法产生花色苷。一致地，功能性SlaN2-样的表达番茄品种中由果实特异性启动子驱动的基因导致整个花色苷生物合成途径的活化以及果皮和果肉中花色苷的高水平积累。两者合计，我们的研究表明，复杂的代谢途径的有效工程改造可以通过组织特异性表达的主转录调节子来实现。