Flavonoids are organic plant compounds which perform a number of important physiological functions related to survival and reproductive success. They are the most important plant pigments for producing the colours designed to attract pollinators. Plant colour is also important for horticulturists as it influences the purchase decisions of consumers. Bright colours are key to ornamental plants, while the red skin and flesh colour of fruit crops are increasingly viewed as indicators of health-giving properties. The FLOWERPOWER project, supported by the Marie Skłodowska-Curie Actions programme, set out to better understand flavonoids and their role in pigmentation to expand breeding options for more colour varieties. Inspired by the recent detection of novel flavonoids in poinsettia, the research adopted breeding techniques informed by genetics, plant biochemistry, plant molecular biology, analytics and bioinformatics. “Closing important knowledge gaps for the biosynthesis of flavonoids has the potential to contribute to future biotechnological approaches in plant breeding,” says Heidi Halbwirth, the coordinator of FLOWERPOWER from the Technical University of Vienna (TU Wien), Austria. The project has generated one successful patent application and two prototype plants with novel enzyme activity and/or colouration. The findings have also resulted in eight articles in peer-reviewed journals, and 165 transcriptomes have been made publicly available for research purposes.
The flavonoid pathway
For the team behind FLOWERPOWER, the existence of white poinsettia leaves, known as bracts, was scientifically perplexing. “The fact that it could not be explained simply by the absence of one of the structural genes pointed to a general scientific problem. Understanding this could help breeders to speed up the breeding process,” adds Halbwirth. To study the flavonoid pathway for poinsettia pigment formation, the chemical profiles of red and white poinsettia bracts were analysed in detail using a variety of analytical methods. These methods included: high-performance liquid chromatography; proton nuclear magnetic resonance-based metabolomics; and liquid chromatography–mass spectrometry. Selected genes were isolated from 38 poinsettia samples and the biochemical instructions for the rare orange-red colouration were unravelled using RNA-Seq analysis. By characterising how the pathways involved in the transition of green leaves to these coloured bracts were regulated, the instructions for different colouration were revealed. “This helped us finally explain the ‘white poinsettia paradox’ – how can white varieties exist when the gene expression and all enzyme activity involved in the formation of red pigments suggest the resulting red bract colouration should be predetermined,” explains Halbwirth.
For a new breed of breeders
Using CRISPR/Cas9 genome editing, the team achieved the first genome-edited poinsettias with the rare and increasingly popular orange colour. These orange-red prototypes will be used in subsequent breeding programmes. They also used a transgenic approach, to develop techniques for breeding blue poinsettia, popular with commercial breeders. Additionally, new breeding approaches identified a novel gene involved in the formation of yellow flavonols, revealing the relevance of genes for the establishment of pigments responsible for yellow colouration. “Our biotechnology approaches to plant breeding research will promote innovation which offers exciting alternatives beyond the traditional cash cows, benefiting consumers and horticulture in general,” notes Halbwirth.
FLOWERPOWER, breed, horticulture, leaves, poinsettias, biotechnology, genes, colouration, pigments, flavonoids, plants, CRISPR/Cas9