Turning red
Plants are wonderful chemical factories. So when synthetic food dyes get banned it is only logical to look for plant produced alternatives, like betalain which is naturally produced by beetroots and their relatives. A new study by American researchers explores the possibility of getting other plant species to produce betalain.
Betalains are behind your red stained fingers after peeling or cutting beetroots. They make an excellent alternative to synthetic red food dyes. The only problem, beetroots don’t store well. To both increase betalain production and storability the researchers explored if they could get other plants to produce it, focussing on Arabidopsis, tobacco and soybean.
Beetroots produce betalain via L-DOPA from tyrosine. So, to get other plants to produce betalain researchers have roughly two approaches. The first is they give the plants just the genes needed for the production of betalain from tyrosine. This is called the “pull” approach as it is pulling tyrosine away from its regular downstream use. The second approach is called a “Push & Pull” approach as it is in addition to pulling tyrosine away, it is also pushing the production of tyrosine upwards, using this approach the researchers also give the plants the instructions to produce extra tyrosine. The researchers wanted to analyse the effects of each approach separately, but for simplicity I focus here in the “Push & Pull” approach.
Ruby red plants
At first, the researchers failed miserably, no stable transgenic betalain producing plants could be produced. Investigating this the researchers found out that while L-DOPA was produced this wasn’t used to produce betalain. So, they did some tweaking to the construct they gave the plant so that it would produce about twice the amount of the enzymes needed for the production of betalain from L-DOPA then the amount of the enzymes it produced for the production of L-DOPA from tyrosine. This seemed to do the trick. The plants with the “Push & Pull” construct turned their stems and leaves ruby red.
For tobacco plants this worked reasonably well, although they where slightly smaller than normal tobacco plants. For soybeans this approach appeared to work even better, with no hint of a smaller statue. However not all seeds of the next generation germinated and the ones that did where hemizygous, meaning that they inherited only one copy of the “Push & Pull” construct. While this is no problem for the current generation, it means that not all seeds of the subsequent generation will carry the genes needed to produce betalain. For Arabidopsis it didn’t work out that well. The freshly transformed plants, although ruby coloured, had lots of growth defects and failed to produce any seeds.
Some extra tweaking needed
So, although the betalain production worked well in soybean and tobacco, there where still some things to optimise. The growth defects and the inability to produce viable seeds suggest toxicity. This toxicity likely occurs through a build up of produced precursors and intermediates and damages the plant. This suggests that the timing of when the extra tytosine production starts and when the production of betalain starts needs to be better coordinated, for example with constructs that start the extra tyrosine production only after the seeds have germinated. This is one of the things that the researchers plan to test next.
So, it is possible to get other plant species to produce the ruby red betalain. However, as this study shows not all species are equally well suited for it. But before betalain can be produced at scale by other plants than beetroot, there is still some tweaking of the “Push & Pull” approach to be done. So that each generation of ruby red plants are just as likely to germinate and inherit the betalain producing genes as the previous one.
Literature
Soyoung Jung, Marcos V V de Oliveira, Ray Collier, Abou Yobi, Ruthie Angelovici, Shawn M Kaeppler, Hiroshi A Maeda, Chassis Selection and Metabolic Fine-Tuning Enable Efficient in planta Betalain Production, Plant Physiology, 2026;, kiag337, https://doi.org/10.1093/plphys/kiag337
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