de Vetten N, ter Horst J, van Schaik H P, de Boer A, Mol J, Koes R
Department of Genetics, Institute for Molecular Biological Sciences, Vrije Universiteit, BioCentrum Amsterdam, de Boelelaan 1087, 1087 HV Amsterdam, The Netherlands.
Proc Natl Acad Sci U S A. 1999 Jan 19;96(2):778-83. doi: 10.1073/pnas.96.2.778.
The substitution pattern of anthocyanin pigments is a main determinant of flower color. Flavonoid 3',5'-hydroxylase (F3'5'H) is a cytochrome P450 enzyme (Cyt P450) that catalyzes the 3', 5'-hydroxylation of dihydroflavonols, the precursors of purple anthocyanins. Species such as rose and carnation lack F3'5'H activity and are, therefore, unable to generate purple or blue flowers. Petunia, on the other hand, contains two loci, termed hf1 and hf2, that encode a Cyt P450 with F3'5'H activity. Here we report the identification of an additional petunia gene that is required for 3',5' substitution of anthocyanins and purple flower colors. It encodes a cytochrome b5 and is expressed exclusively in the flower. Inactivation of the gene by targeted transposon mutagenesis reduced F3'5'H enzyme activity and the accumulation of 5'-substituted anthocyanins, resulting in an altered flower color. However, no phenotypic effect on the activity of other Cyt P450s, involved in the synthesis of hormones or general phenylpropanoids, was observed. These data provide in vivo evidence for the regulation of the activity of specific Cyt P450s by a cytochrome b5.
花青素色素的取代模式是花色的主要决定因素。类黄酮3',5'-羟化酶（F3'5'H）是一种细胞色素P450酶（Cyt P450），它催化二氢黄酮醇（紫色花青素的前体）的3',5'-羟基化反应。玫瑰和康乃馨等物种缺乏F3'5'H活性，因此无法产生紫色或蓝色花朵。另一方面，矮牵牛含有两个基因座，称为hf1和hf2，它们编码具有F3'5'H活性的细胞色素P450。在此，我们报告了矮牵牛中另一个基因的鉴定，该基因是花青素3',5'-取代和紫色花色所必需的。它编码一种细胞色素b5，并且仅在花中表达。通过靶向转座子诱变使该基因失活会降低F3'5'H酶活性以及5'-取代花青素的积累，从而导致花色改变。然而，未观察到对参与激素或一般苯丙烷类化合物合成的其他细胞色素P450活性的表型影响。这些数据为细胞色素b5对特定细胞色素P450活性的调节提供了体内证据。
