Abstract
Potassium (K+) is a key monovalent cation necessary for multiple aspects of cell growth and survival. In plants, this cation also plays a key role in the control of stomatal movement. KAT1 and its homolog KAT2 are the main inward rectifying channels present in guard cells, mediating K+ influx into these cells, resulting in stomatal opening. To gain further insight into the regulation of these channels, we performed a split-ubiquitin protein-protein interaction screen searching for KAT1 interactors in Arabidopsis (Arabidopsis thaliana). We characterized one of these candidates, BCL2-ASSOCIATED ATHANOGENE4 (BAG4), in detail using biochemical and genetic approaches to confirm this interaction and its effect on KAT1 activity. We show that BAG4 improves KAT1-mediated K+ transport in two heterologous systems and provide evidence that in plants, BAG4 interacts with KAT1 and favors the arrival of KAT1 at the plasma membrane. Importantly, lines lacking or overexpressing the BAG4 gene show altered KAT1 plasma membrane accumulation and alterations in stomatal movement. Our data allowed us to identify a KAT1 regulator and define a potential target for the plant BAG family. The identification of physiologically relevant regulators of K+ channels will aid in the design of approaches that may impact drought tolerance and pathogen susceptibility.
Highlights
61 Ion homeostasis is a dynamic process essential for the normal functioning of any organism
We identified BCL248 ASSOCIATED ATHANOGENE4 (BAG4) as a KAT1 interacting protein
Co-expression of BAG4 with KAT1 improved growth under limiting potassium conditions, whereas two other Arabidopsis proteins recovered in the screening, (PPI1 (Proton pump interacting protein 1) and RPT2 (Root phototropism 2)), had no functional effect in this assay
Summary
61 Ion homeostasis is a dynamic process essential for the normal functioning of any organism. Cells must discriminate between the physiologically relevant ions and the toxic ions that may be chemically similar. For this reason, all living organisms have developed efficient systems to capture and store ions and complex mechanisms to maintain homeostatic concentrations. Ion homeostasis must provide the environment required to maintain all internal processes, prevent toxicity and enable the response to environmental changes using the minerals present in the soil. Potassium homeostasis is essential for optimal water use efficiency, as potassium currents participate in stomatal movement. Optimizing water use efficiency of crops by improving the potassium regulation in the guard cell, and improving transpiration regulation, can directly affect food production under adverse conditions (Wang et al, 2014)
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