Serrated leaves
Ever asked yourself the question why the leaves of young plants have a different shape from those of mature plants? In a preprint German researchers now show that this is due to the fact that the protein SPL9 withdraws from the tip of the leaf.
While young leaves often have a round or oval shape, the leaves of mature plants have more serrations or lobes. Some leaves even look like they are made up out of multiple individual leaves.
The round leaf shape of juvenile plants is due to the fact that the protein SPL9 promotes cell division when it is present. In young plants SPL9 is present in the whole area of the leaf, but in contrast, in mature plants SPL9 is mainly present at the base of the leaves. When the researchers caused SPL9 also in juvenile plants to be mainly present at the base of the leaves, then juvenile plants also get serrated leaves.
The contrast between SPL9 at the base and RCO and KNOX1 in the rest of the leaf causes extra serrated leaves
But SPL9 is not the only protein of which is known to influence leaf shape. Two other proteins, KNOX1 and RCO also influence leaf shape. Therefore the researchers decided to analyse their influence on leaf shape in both juvenile and mature plants. The researchers created plants that had a larger amount of these proteins. They noticed that while extra KNOX1 or RCO in the leaves of mature plants amplified the serration, they did not do this in the leaves of juvenile plants.
Still it is not that simple that only the absence of SPL9 causes serrated leaves. It turns out that that it is the contrast that is needed of having both lots of SPL9 at the leaf base and nerves, and in its absence the free rein of RCO and KNOX1 in the rest of the leaf. The researchers noticed this when the analysed plants that produced more SPL9 as well as more RCO. Then the leaves were more serrated, but not only in the mature plants, not the juvenile ones.
Literature
Xin-Min Li, Hannah Jenke, Sören Strauss, Yi Wang, Neha Bhatia, Daniel Kierzkowski, Rena Lymbouridou, Peter Huijser, Richard S. Smith, Adam Runions, Miltos Tsiantis (2024) Age-associated growth control modifies leaf proximodistal symmetry and enables leaf shape diversification. BioRxiv: doi: https://doi.org/10.1101/2024.04.02.587754
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