A cytochromeb₅is required for full activity of flavonoid 3′,5′-hydroxylase, a cytochrome P450 involved in the formation of blue flower colors

Abstract

The substitution pattern of anthocyanin pigments is a main determinant of f lower color. Flavonoid 3,5-hydroxylase (F35H) is a cytochrome P450 enzyme (Cyt P450) that catalyzes the 3,5-hydroxylation of dihydrof lavonols, the precursors of purple anthocyanins. Species such as rose and carnation lack F35H activity and are, therefore, unable to generate purple or blue f lowers. Petunia, on the other hand, contains two loci, termed hf1 and hf2, that encode a Cyt P450 with F35H activity. Here we report the identification of an additional petunia gene that is required for 3,5 substitution of anthocyanins and purple f lower colors. It encodes a cytochrome b 5 and is expressed exclusively in the f lower. Inactivation of the gene by targeted transposon mutagenesis reduced F35H enzyme activity and the accumulation of 5-substituted anthocyanins, resulting in an altered f lower 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 b 5 .

Proteins involved in biotic and abiotic stress responses as the most significant biomarkers in the ripening of Pinot Noir skins

“…A possible involvement of Cytb5 in the determination of flower color was also described: de Vetten and collegues (de Vetten et al 1999) reported that the inactivation of the relative gene by transposon mutagenesis resulted in a reduced 3′,5′ substi-tution of anthocyanins. In this work, we describe for the first time, to our knowledge, the discovery of this protein in grape skins.…”

anthocyanin1 of Petunia Encodes a Basic Helix-Loop-Helix Protein That Directly Activates Transcription of Structural Anthocyanin Genes

“…Previous experiments had shown that an1 Ϫ petals lack transcripts of at least nine structural anthocyanin genes (see, e.g., Quattrocchio et al, 1993;Kroon et al, 1994;de Vetten et al, 1999) and of one potential regulatory gene, Pmyb27, which encodes a protein with similarity to MYB-domain transcription factors (Mur, 1995). Thus, AN1 might induce dfr transcription directly (e.g., as part of the transcription complex on the dfr promoter) or indirectly (by inducing the expression of an intermediate regulator such as MYB27).…”

Exploiting the Versatility of Human Cytochrome P450 Enzymes: The Promise of Blue Roses From Biotechnology

“…P450s are important catalysts in the anthocyanin pathway, one arm of which leads to the formation of blue delphinidin-derived pigments in such owers as petunias (34). The P450s critically involved here catalyze the 3 0 -and 5 0 -hydroxylation of the anthocyanin B ring but require a cytochrome b 5 for full 5 0 hydroxylase activity (33). Moreover, the pigments are localized in vacuoles, the pH of which critically in uences pigment color.…”

“…Other applications can also be envisaged, such as the in situ production of pigment in plant tissue, speci cally owers (e.g., ower crops) and bre (e.g., cotton) (33,34). The "Holy Grail" of horticulture is the blue rose; such a novelty as an engineered blue rose could impact signi cantly on the cut-ower market for roses, which is worth over $5 billion per year in the United States alone (35).…”