New plants

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New plants

Plants reproduce through pollination. But they can do it also without. For example, can you multiply plants via cuttings. The cuttings are a clone of the mother plant. You can also do this on a much smaller scale. Take mature cells, from for example a leaf, and grow them on culture media and under the right conditions these mature cells will take on an embryo-cell identity. Researchers call this process somatic embryogenesis. It is a well-known technique used by breeders for multiplying plants. But we actually don’t really know what the underling mechanism of this process is. Dutch researchers are trying to change this.

Specifically, the researchers focused on the role of endogenous auxin. Of this plant hormone it is known that it is required for normal embryos to develop from a ball of cells into the shape of a plant. But it is not really clear what its job during somatic embryogenesis. More so because synthetic auxin is also needed during the process of acquiring the embryonic cell fate.

The first thing the researchers did was determine when the cells get their embryonic cell identity. This they did using an embryo specific marker WOX2. The researchers observed lighting up of the marker after 5 to 6 days only in cells growing on medium with the synthetic auxin. Those cells developed into a kind of pro-embryos. But only after transfer to medium without synthetic auxin did the pro-embryos develop into clearly distinguishable globular embryos, the ball of cells. And subsequently developed just like normal embryos.

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Endogenous auxin is clearly needed to keep the acquired embryogenic cell identity

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To find out the role of endogenous auxin in all this, the researchers looked to auxin synthesis. They observed that the auxin synthesis genes were turned on from day 7, when the cells had acquired their embryonic cell identity. Blocked the researchers the ability to turn on these auxin synthesis genes, then the cells lost their embryonic cell identity. Production of endogenous auxin is a thus a requirement for maintaining embryonic cell identity.

But control of the distribution of auxin is also needed for the development from a ball of cells into a plant. When the researchers blocked the ability of the cell to take up auxin, then these cells also lost their embryogenic cell identity. But the ability to pump auxin out of the cell had no influence on this. The cells kept their embryogenic cell identity when blocking of the auxin efflux pumps, but they lost the ability to develop from a ball of cells into a plant.

Endogenous auxin is clearly needed to keep the acquired embryogenic cell identity. Now this is known, breeders can use this to improve the procedure of multiplying plants through embryogenesis. But the question remains what happens in those first 5 to 7 days during which the cell acquires its embryogenic cell identity.

Literature

Karami, O., Philipsen, C., Rahimi, A., Nurillah, A.R., Boutilier, K. and Offringa, R. (2023), Endogenous auxin maintains embryonic cell identity and promotes somatic embryo development in Arabidopsis. Plant Journal, 113: 7-22. https://doi.org/10.1111/tpj.16024