Sucrose-induced Receptor Kinase 1 is Modulated by an Interacting Kinase with Short Extracellular Domain

Area of Science:

• Plant Physiology
• Molecular Biology
• Biochemistry

Background:

• Sucrose is the primary carbohydrate translocated for plant growth.
• Water uptake via aquaporins is crucial for cell expansion in non-photosynthetic organs.
• Sucrose Induced Receptor Kinase 1 (SIRK1) regulates aquaporin activity through phosphorylation.

Purpose of the Study:

• To investigate the regulatory role of AT3G02880 (QSK1) in modulating SIRK1 activity.
• To elucidate the molecular mechanism by which QSK1 influences sucrose-induced aquaporin function.

Main Methods:

• Phosphoproteomics analysis of single and double mutants (sirk1, qsk1, sirk1 qsk1).
• In vitro kinase assays to study receptor kinase interactions and phosphorylation events.
• Root protoplast swelling assays to measure water influx rates.

Main Results:

• SIRK1 autophosphorylates at Ser-744 upon sucrose treatment.
• Activated SIRK1 interacts with and transphosphorylates QSK1 and QSK2.
• The qsk1qsk2 mutant exhibits reduced water influx under sucrose stimulation.
• Phosphoproteomics data indicate aquaporin phosphorylation is dependent on the SIRK1-QSK1 complex.

Conclusions:

• QSK1 acts as a coreceptor, stabilizing and enhancing SIRK1 activity.
• The SIRK1-QSK1 complex is essential for regulating aquaporin phosphorylation and water uptake.
• This pathway is critical for coordinating carbohydrate supply with water transport during plant growth.