Maybe orange will be possible
For lots of flower breeders have one wish: breeding a flower with a unique colour. This allows their flower to stick out in a bunch of flowers. Despite their wish to be unique, some colours remain unattainable. Simply because the plant does not have the enzymes to make that specific colour. For example, without human intervention there are no blue roses, and no orange petunias. Although, we might be mistaken for that last one. Finnish and Dutch researchers showed that there are only a few adaptations needed to get orange flowers.
Petunia flowers get their colour from anthocyanin. These colour the flowers in shades between pink and purple, whereby the precise colour depends for a part on the anthocyanin variant present. One colour that they do not show is orange. This is due to the preference of one of the enzymes needed to make anthocyanins. This enzyme prefers the precursor of the pink/purple variant and does not work with the precursor of the orange variant.
To find out if they could change the preference if this enzyme, the researchers studied the part of the enzyme that grabs its substrate. By comparing this part of the petunia enzyme with that of comparable parts of enzymes that do work with the precursor of the orange anthocyanin the researchers discovered three points that were different in the petunia enzyme.
A subtle colour change from pink to orange
Subsequently the researchers tested if changing these points in the petunia enzyme results in an enzyme that does use the orange precursor as substrate. They did this by doing two tests. In the first test the researchers produce the three versions of the enzyme in tobacco plants. These they extracted and use them to test their substrate preference. Here they noticed that two of the three variants now prefer the precursor of the orange anthocyanin.
To test if this preference also holds in the plant, the researchers introduced those three enzyme variants in petunia plants. While plants without the adapted enzyme had light pink flower, those with the adapted variant with a preference for the orange precursor had an orange hue.
The change in flower colour was not as dramatic as the researchers had hoped for. However, it does show that with only a few changes an orange colour is indeed one of the possibilities. Maybe in the future we might see those orange petunias on the marked after all.
Literature
Vainio J, Mattila S, Abdou SM, Sipari N and Teeri TH (2023) Petunia dihydroflavonol 4-reductase is only a few amino acids away from producing orange pelargonidin-based anthocyanins. Front. Plant Sci. 14:1227219. https://doi.org/10.3389/fpls.2023.1227219
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