Potential for regeneration
Some cells have the potential to be come everything they wish, they are totipotent. Like the zygote, the cell that forms after the melting of the female and male gametes. But from plants it is known that more cell types can develop into totipotent cells. You can see this possibility for example in leaf cells. Under specific circumstances they can develop embryo’s.
For a long time, the question was if all plant cells could develop into embryo’s or that only specific cells can do that. Now a group of international researchers show in their paper “Time-resolved reprogramming of single somatic cells into totipotent states during plant regeneration” that only specific cells have this possibility to develop into embryo’s.
For the study the researchers used an embryo inducing line. These plants develop embryos on their leaves after the researchers activate the gene LEC2. To find out if there are specific cells from which those embryos develop, the researchers zoomed in on the leaf cells. This enabled them to see that the cells from which embryo’s developed, first divided anticlinal. This was followed by one of the daughter cells dividing asymmetrically in three. These three cell subsequently developed into an embryo.
Local auxin maximum
The first question the researchers wanted to answer was how. Which genes and hormones are directing this? To answer that question the researchers studied the presence of the hormone auxin. Using an auxin receptor coupled to a fluorescent protein, the researchers observed that in the cells just before they start to develop towards an embryo, there is a large amount of auxin present.
The researchers also checked what the gen YUC, involved in auxin production, does. After activation of LEC2, this gene for auxin biosynthesis became active. But only in cells that subsequently developed into embryos. The researchers also looked at what happens in plants that do not have any YUC. There the researchers observed that even when LEC2 was active, no embryos developed.
Subsequently the researchers asked which cells have the possibility of becoming totipotent after LEC2 activation. The researchers had noticed that when LEC2 was active and embryos developed at the same time less stomata developed. Therefore, the researchers followed what happens to cells from which stomata develop. For this the researchers coupled marker genes for each of the sub-stages of stomata development to a fluorescent protein.
Stomata
In this way the researchers noticed that upon activation of LEC2 leaf cells who where early in the development towards stomata reacted to LEC2 and switched to developing embryos. While leaf cells that were further in the process of stomata development just continued on that path.
The researchers also studied what happens when there is more of the early stomata development marker gene SPCH. This, so observed the researchers, resulted not only in more embryo development on the leaves after activation of LEC2, but also on the stem and roots. But only if those plants could produce also auxin to create local auxin gradients.
Lastly the researchers looked at hoe LEC2 together with SPCH is regulating the auxin production. They discovered that LEC2 and SPCH work together. In this LEC2 recognises the activation region of the auxin biosynthesis genes but needs SPCH to actually activate those. In the absence of SPCH LEC2 is even dimming the activity of the auxin biosynthesis genes.
In this way the researchers show that only plant cells that already have a certain amount of totipotency can be tricked into developing embryos. In young leaves this are the cells that are destined to become stomata.
Literature
Tang et al., Time-resolved reprogramming of single somatic cells into totipotent states during plant regeneration, Cell (2025), https://doi.org/10.1016/j.cell.2025.08.031
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