Decoy for cytokinin
Hormone signalling is regulated in multiple ways. Now researchers in Molecular Plant show a new way: using a decoy to regulate cytokinin signalling.
The use of a decoy in the form of non-functioning receptors is known strategy in mammalian cells. But in plants this was up till now unknown. The researchers stumbled on it by accident when they cloned the cytokine receptor CRE1. A few of the clones contained the seventh intron of the gene, resulting in a frame shift and an early stop codon. The consequence: it can bind cytokinin, but it can’t initiate the cytokinin signalling cascade, it is missing the responsible domain.
Closer study showed that under normal conditions 2 to 3 % of all CRE1 proteins are those of the shorter version. But that when the amount of cytokinin increases that also the amount of shorter CRE1 version increases.
The shorter CRE1 functions as a decoy
Subsequently the researchers studied where the shorter CRE1 version is located in the cell. These was just as its normal version located in the membrane of the ER. There they pair up with other CRE1 proteins (either the long or short version) or other cytokinin receptors.
The question was what is shorter version of CRE1 doing. To investigate this the researchers analysed how plants react to cytokinin. When the normal CRE1 version is present, then there is a clear cytokinin signal, cytokinin decreases root growth. Plants that had a lot of the shorter CRE1 version hardly reacted to cytokinin, their roots grew just as fast as those of plants that had not received any cytokinin.
The shorter CRE1 is capturing the cytokinin signal, it does this by binding cytokinin but not initiating the signalling cascade. It lures cytokinin away from the functioning receptors. An elegant way for preventing cytokinin signalling getting out of hand.
Literature
Králová M., Kubalová I., Hajný J., Kubiasová K., Vagaská K., Ge Z., Gallei M., Semerádová H., Kuchařová A., Hönig M., Monzer A., Kovačik M., Friml J., Novák O., Benková E., Ikeda Y., and Zalabák D. (2024). A decoy receptor derived from alternative splicing fine-tunes cytokinin signaling in Arabidopsis. Mol. Plant. doi: https://doi.org/10.1016/j.molp.2024.11.001.
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