Abstract
Sucrose as a product of photosynthesis is the major carbohydrate translocated from photosynthetic leaves to growing nonphotosynthetic organs such as roots and seeds. These growing tissues, besides carbohydrate supply, require uptake of water through aquaporins to enhance cell expansion during growth. Previous work revealed Sucrose Induced Receptor Kinase, SIRK1, to control aquaporin activity via phosphorylation in response to external sucrose stimulation. Here, we present the regulatory role of AT3G02880 (QSK1), a receptor kinase with a short external domain, in modulation of SIRK1 activity. Our results suggest that SIRK1 autophosphorylates at Ser-744 after sucrose treatment. Autophosphorylated SIRK1 then interacts with and transphosphorylates QSK1 and QSK2. Upon interaction with QSK1, SIRK1 phosphorylates aquaporins at their regulatory C-terminal phosphorylation sites. Consequently, in root protoplast swelling assays, the qsk1qsk2 mutant showed reduced water influx rates under iso-osmotic sucrose stimulation, confirming an involvement in the same signaling pathway as the receptor kinase SIRK1. Large-scale phosphoproteomics comparing single mutant sirk1, qsk1, and double mutant sirk1 qsk1 revealed that aquaporins were regulated by phosphorylation depending on an activated receptor kinase complex of SIRK1, as well as QSK1. QSK1 thereby acts as a coreceptor stabilizing and enhancing SIRK1 activity and recruiting substrate proteins, such as aquaporins.
Highlights
This page was generated automatically upon download from the ETH Zurich Research Collection
This work aimed at a close investigation of the functional role of QSK1 (AT3G02880) and its close homolog QSK2 (AT5G16590) in the complex with SUCROSE INDUCED RECEPTOR KINASE 1 (SIRK1, AT5G10020) during regulation of aquaporins in response to external changes in sucrose concentrations
These results confirm that SIRK1 forms a complex with QSK1, and this interaction is enhanced under sucrose stimulation
Summary
This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. Authors Xu Na Wu, Liangcui Chu, Lin Xi, Heidi Pertl-Obermeyer, Zhi Li, Kamil Sklodowski, Clara Sanchez-Rodriguez, Gerhard Obermeyer, and Waltraud X. The activation of aquaporins by a receptor kinase complex of SIRK1 and QSK1 was studied in detail. Pulldown studies and physiological experiments we conclude that SIRK1 may function as a main receptor which forms a complex with coreceptor QSK1. Phosphorylated QSK1 enhanced and stabilized the interaction with aquaporins as substrates of the receptor kinase complex. Author’s Choice los Sucrose-induced Receptor Kinase 1 is Modulated by an Interacting Kinase with Short Extracellular Domain*□S
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