Flowers on stalks
Dandelions, daisies, but also the by researchers much loved tale cress, they all grow their leaves in a rosette. There is hardly a piece of stem between the leaves. The stem only starts growing when the plants start flowering. But the researchers noticed for tale cress, that when they grow in the dark, the rosette disappears. Resulting in clearly visible pieces of stem between the leaves. Now researchers for the Netherlands have found out whey these plants grow rosette leaves in the light.
Plants grow from their growth centres. Here a small group of slowly dividing stem cells is located. After each division one of the daughter cells is pushed outside the group. These outside the stem-cell located cells are together responsible for forming the shoot and leaves. Only by rosette forming plants, there is a brake on the cells that are destined to become the shoot. The gene on/off switch ATH1 prevents that these shoot-cells can stretch-out, but does this only in the light.
To study the influence of the light on ATH1, the researchers studied rosette formation in plants that did not perceive any light. They noticed that those plants did not form a rosette, pieces of stem between the leaves were clearly visible. Just as if they grew in the dark.
The ATH1-PIF switch enables rozette formation and flowers on stalks
All light receptors are in contact in COP1, the manager that tells plants when it is dark. When anyone of the light receptors perceives light, then they turn off COP1. Therefore, the researchers studied rosette formation in plants that did not have any COP1. It turned out that these plants also did not form a rosette. In contrast to light perceiving plants, in plants that did not perceive any light the researchers did not see any ATH1 in the cells of the future shoot, they did not have a brake.
It appears that COP1 causes ATH1 to be turned off. But if COP1 was the only manager of ATH1, then researchers expect a gradual transition from rosette forming to non-rosette forming. But this is not what the researchers observed, with a little bit of light the plants still formed rosettes. COP1, the researchers noticed, did something else. In addition to turning off ATH1, COP1 was also turning on PIF-genes. These genes it turned out were switching off ATH1. But because ATH1 is switching of the PIF-genes, there is a balance. Till one of the two gets a majority and switches the switch. If this is ATH1, then a rosette forms, is it PIF, then the shoot becomes visible between the leaves.
In tale cress in the light, like its normal growth conditions, the presence of this switch enables rosette formation. Till the plant gets the urge to flower. Then we get flowers on stalks.
Literature
Shokrian Hajibehzad, S., Silva, S.S., Peeters, N., Stouten, E., Buijs, G., Smeekens, S. and Proveniers, M. (2023), Arabidopsis thaliana rosette habit is controlled by combined light and energy signaling converging on transcriptional control of the TALE homeobox gene ATH1. New Phytol. https://doi.org/10.1111/nph.19014
Plant en Zo 