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bioRxiv · 10.1101/2023.11.06.565614

Cytokinin Dehydrogenase in Xylem Sap Reveals A Direct Link Between Cytokinin Metabolism and Long-Distance Transport

Nedved, D.·Motyka, V.·Raimanova, I.·Dobrev, P. I.·Kopecny, D.·Briozzo, P.·Brunoni, F.·Müller, K.·Hoyerova, K.
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Abstract

Metabolic degradation of plant hormones cytokinins (CKs) co-regulates their homeostasis and signalling. In this work, we employed a large-scale bioinformatical analysis to address a diversity of cytokinin oxidase/dehydrogenase (CKX) substrate specificities previously described in several case studies. We present a three-way correlation of the entire CKX amino acid sequences, a variable motif involved in substrate binding, and subcellular localizations predicted by a deep learning model. This correlation is conserved in monocotyledonous plants, suggesting that the CKX diversity in a single species allows a precise tuning of the CK homeostasis. Following these findings, we detected CKX activity in xylem sap for the first time, using the oat (Avena sativa) as a model plant. Further investigation of the substrate specificity and glycosylation of this xylem-located CKX suggested that it originates in roots. We have identified 27 putative CKXs in oats and attributed the xylem-located activity to the extracellular isoforms AsCKX1a,c,d. Finally, we show that the xylem-located CKX activity responds to the nitrate supply, highlighting its physiological relevance. Taken together, we show that CKX directly modulates root-to-shoot CK translocation through metabolic degradation of the transported CKs.

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Nedved, D., Motyka, V., Raimanova, I., Dobrev, P. I., Kopecny, D., Briozzo, P., Brunoni, F., Müller, K., Hoyerova, K.. 2023-11-06. Cytokinin Dehydrogenase in Xylem Sap Reveals A Direct Link Between Cytokinin Metabolism and Long-Distance Transport. https://doi.org/10.1101/2023.11.06.565614

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