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Producing new plants without sowing

Producing offspring of a crop without sowing and that is even bigger than the parent plant. According to Leiden researchers this can be achieved by overstimulating a single gene that rejuvenates cells, including bringing them back to the embryonic phase.

‘The AHL15 gene was initially discovered by colleague Bert van der Zaal, who is also co-author on our publication in the May 4th issue of Nature Communications’, tells Remko Offringa of the Institute of Biology Leiden.

‘He took a closer look at overexpression of the gene in the model plant Arabidopsis thaliana, which means that he expressed the gene at a higher level and in different places in the plant than normal. When he took a closer look, he observed embryos on the cotyledons, the first leaves of a germinating seedling, which means that cells in those cotyledons went back in development to the embryonic phase’, says Offringa. ‘Those embryos can germinate and develop into new plants that are identical to the parent plant, something that would not be possible with fully developed (differentiated) plant cells.’

New embryos grow on the two cotyledons

Forever young by cloning

The results in Arabidopsis create new possibilities for propagating crops. In many cases, growers cultivate hybrid crops that are generated by crossing two different parental plants. By implementing this discovery, this crossing will no longer be necessary, as the hybrid crop can be maintained or kept ‘forever young’ by simply cloning it through the embryos that develop on the plant.

The AHL15 gene is not unique in this aspect, however. ‘Many companies are already investigating the use of the so-called BABY BOOM gene, or in short BBM, for this purpose. Together with researchers at Wageningen University and Research we showed that the BBM protein controls expression of our AHL15 gene’, explains Offringa. ‘So it is not clear whether plant breeders will use our gene for propagating hybrid crops, since they already actively look at BBM. However, overexpression of both AHL15 and BBM might have benefits for some applications’.

Under a special microscope the chromosomes light up

Unique: chromosome duplication

First author Omid Karami discovered another, unique aspect of AHL15 overexpression. Using a fluorescent reporter and a confocal microscope he observed a complete duplication of chromosomes in some of the embryonic cells.

‘He found out that this is the result of how DNA strands behave after overexpression of AHL15’, states Offringa. ‘Normally, DNA is freely spread through the cell nucleus, until cell division takes place. Then it condensates into tightly wound strings and the individual chromosomes become discernible. This makes it possible during cell division to correctly distribute the duplicated DNA over the two daughter cells. However, Karami observed that this condensation of DNA is incomplete when AHL15 is overexpressed. As a result, chromosome segregation fails, and one daughter cell remains with a duplicated set of chromosomes. This is what we call polyploidization.’

Yield and evolution

Polyploidization is a frequently used tool in crop breeding, generally resulting in bigger plants and fruits and thus in more yield. As such, the research can contribute to the UN sustainable development goal 2 (SDG2), zero hunger. In addition, the researchers think the findings can make an important contribution to the fundamental understanding of evolution. ‘In evolution biology a correlation has been observed between genome duplication and the origin of new species. Genome duplication reduces the selection pressure on individual genes and as a result mutations can occur with which a plant can reprogram genetically and adjust itself more quickly to a changing environment.

The first author of the current paper, Omid Karami, already discovered that the gene can extend plant longevity and won an award for this. But it would also be good to know whether AHL15 can also cause polyploidization in nature and thus has a role in speciation. ‘That creates possibilities for our follow-up research’, concludes Offringa.

The publication of May 4th in Nature Communications.

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