Recent progress of flower colour modification by biotechnology

Abstract

Genetically-modified, colour-altered varieties of the important cut-flower crop carnation have now been commercially available for nearly ten years. In this review we describe the manipulation of the anthocyanin biosynthesis pathway that has lead to the development of these varieties and how similar manipulations have been successfully applied to both pot plants and another cut-flower species, the rose. From this experience it is clear that down- and up-regulation of the flavonoid and anthocyanin pathway is both possible and predictable. The major commercial benefit of the application of this technology has so far been the development of novel flower colours through the development of transgenic varieties that produce, uniquely for the target species, anthocyanins derived from delphinidin. These anthocyanins are ubiquitous in nature, and occur in both ornamental plants and common food plants. Through the extensive regulatory approval processes that must occur for the commercialization of genetically modified organisms, we have accumulated considerable experimental and trial data to show the accumulation of delphinidin based anthocyanins in the transgenic plants poses no environmental or health risk.

Keywords: anthocyanin; flavonoid; flower colour; genetic engineering; genetically modified organism (GMO).

Figure 1.

Commercialized transgenic carnation (a) and rose (b) cultivars producing delphinidin and having blue hue that hybridization breeding has not achieved. The transgenic carnation and rose also contain selectable marker genes; for herbicide resistance in carnation and antibiotic resistance in rose.

Scheme 1.

(a) The biosynthetic pathway leading to the biosynthesis of the anthocyanidin. Anthocyanidin is further modified with glycosyl, acyl, or methyl groups catalysed by glycosyltransferase, acyltransferase and methyltransferase as described in the text. The typical color that each anthocyanidin tend to give is shown, but the actual color depends on various factors as described in the text. Note that though the positions of methylation on the B-ring are shown, methyl groups are added to anthocyanins, not to anthocyanidins. Abbreviations: CHS, chalcone synthase; F3H, flavanone 3-hydroxylase; F3′H, flavonoid 3′-hydroxylase; F3′5′H, flavonoid 3′,5′-hydroxylase; DFR, dihydroflavonol 4-reductase; ANS, anthocyanidin synthase; MT, methyltransferase, GT, glucosyltransferase; AT, acyltransferase; FNS, flavone synthase; FLS, flavonol synthase. (b) Typical blue polyacyl anthocyanins; gentiodelphin from Gentiana triflora and ternatin A1 from Clitoria ternatea.