Breeding poinsettias with novel bract colouration by genome editing

Abstract

Poinsettia (Euphorbia pulcherrima) commonly shows red bract colouration caused by theaccumulation of cyanidin-type anthocyanins. Orange-red cultivars, which accumulatepelargonidin-type anthocyanins occur rarely, whereas blue poinsettias are not naturally presentdue to the lack of delphinidin formation. Breeding is an arduous process, and a lot of effort isnecessary to obtain plants with desired traits. Some phenotypes are not possible to achieve byclassical breeding approaches due to limitations in the genetic background of the plants.Molecular breeding techniques like genome editing can help to overcome those obstacles andobtain novel poinsettia varieties with orange or blue colour in a fast and efficient way. Thecolour of anthocyanin pigments depends on the B-ring hydroxylation pattern and ranges fromorange pelargonidin (one hydroxyl group), dark red to pink cyanidin (two hydroxyl groups)and blue to violet delphinidin (three hydroxyl groups). Two factors are crucial for theestablishment of the B-ring hydroxylation pattern. First, the presence or absence of flavonoid3’-hydroxylase (F3’H) and flavonoid 3’5’-hydroxylase (F3’5’H) activity, and second, thesubstrate specificity of dihydroflavonol 4-reductase (DFR), which provides importantintermediates in the formation of anthocyanins. In this thesis, the physiological background ofcolour formation was studied in petunia as a model plant and in red, and orange poinsettiacultivars. Based on this, a strategy for molecular breeding of orange and blue poinsettia wasestablished. The investigations on the molecular background of pigment formation in orange