Engineering of the Rose Flavonoid Biosynthetic Pathway Successfully Generated Blue-Hued Flowers Accumulating Delphinidin

Abstract

Flower color is mainly determined by anthocyanins. Rosa hybrida lacks violet to blue flower varieties due to the absence of delphinidin-based anthocyanins, usually the major constituents of violet and blue flowers, because roses do not possess flavonoid 3',5'-hydoxylase (F3'5'H), a key enzyme for delphinidin biosynthesis. Other factors such as the presence of co-pigments and the vacuolar pH also affect flower color. We analyzed the flavonoid composition of hundreds of rose cultivars and measured the pH of their petal juice in order to select hosts of genetic transformation that would be suitable for the exclusive accumulation of delphinidin and the resulting color change toward blue. Expression of the viola F3'5'H gene in some of the selected cultivars resulted in the accumulation of a high percentage of delphinidin (up to 95%) and a novel bluish flower color. For more exclusive and dominant accumulation of delphinidin irrespective of the hosts, we down-regulated the endogenous dihydroflavonol 4-reductase (DFR) gene and overexpressed the Irisxhollandica DFR gene in addition to the viola F3'5'H gene in a rose cultivar. The resultant roses exclusively accumulated delphinidin in the petals, and the flowers had blue hues not achieved by hybridization breeding. Moreover, the ability for exclusive accumulation of delphinidin was inherited by the next generations.

Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits

“…It appears as a blue-reddish or purple pigment in the plant. The blue hue of flowers is due to the delphinidin pigment [6]. Pelargonidin differs from most of the anthocyanidins.…”

“…However, there has some exception. Although delphinidin is a purple-colored pigment, the blue hue of flower could be due to the delphinidin pigment in higher pH conditions [6]. At higher pH or alkaline conditions, for example, petanin is resistant to degradation even at pH 8 [18].…”

Isolation of Dihydroflavonol-4-reductase (DFR) Gene in Dendrobium helix cv. Pomeo Brown

“…This showed that DFR enzymes from varied flower color might have different structure. The difference of DFR enzymes catalyzed product is due to substrate differences [11]. The specific catalytic activity character of DFR enzyme is caused by amino acid residue in the specific active sites [18].…”

“…One of the most interesting characteristics concerning the known DFR enzymes is their substrate specificity. DFR proteins of many plants can accept dihydroflavonols with different hydroxylation patterns like dihydrokaempferol (DHK), dihydroquercetin (DHQ), and dihydromyricetin (DHM) as substrates [11][12][13]. On the other hand, DFR activities to convert one or more substrate of dihydroflavonols were said to be low in some postulated species.…”

A chimeric repressor of petunia PH4 R2R3-MYB family transcription factor generates margined flowers in torenia

“…In addition, many genes and promoters must usually be tested to find a proper construct which successfully catalyzes anthocyanin modification. 23,24 Even after all this effort, anthocyanin color is never truly blue, but is more usually purple or violet.…”