Abstract
Stomata are the main gateways for water and air transport between leaves and the environment. Inward-rectifying potassium channels regulate photo-induced stomatal opening. Rice contains three inward rectifying shaker-like potassium channel proteins, OsKAT1, OsKAT2, and OsKAT3. Among these, only OsKAT2 is specifically expressed in guard cells. Here, we investigated the functions of OsKAT2 in stomatal regulation using three dominant negative mutant proteins, OsKAT2(T235R), OsKAT2(T285A) and OsKAT2(T285D), which are altered in amino acids in the channel pore and at a phosphorylation site. Yeast complementation and patch clamp assays showed that all three mutant proteins lost channel activity. However, among plants overexpressing these mutant proteins, only plants overexpressing OsKAT2(T235R) showed significantly less water loss than the control. Moreover, overexpression of this mutant protein led to delayed photo-induced stomatal opening and increased drought tolerance. Our results indicate that OsKAT2 is an inward- rectifying shaker-like potassium channel that mainly functions in stomatal opening. Interestingly, overexpression of OsKAT2(T235R) did not cause serious defects in growth or yield in rice, suggesting that OsKAT2 is a potential target for engineering plants with improved drought tolerance without yield penalty.
Highlights
Cationic nutrients such as K+, Ca2+, and Mg2+ are essential for physiological processes such as plant growth and cellular homeostasis (Dreyer and Uozumi, 2011)
OsKAT2 is expressed in rice guard cells, where it might function as an inward rectifying shakerlike potassium channel and might be a functional ortholog of Arabidopsis AtKAT1 (Hwang et al, 2013)
We constructed three proteins with single amino-acid mutations at these two threonine sites, including threonine substituted with arginine (T235R), alanine (T285A) and aspartic acid (T285D), and performed a complementation assay using K+ uptake-deficient yeast strain, CY162, which was previously reported to be complemented by OsKAT2 (Hwang et al, 2013)
Summary
Cationic nutrients such as K+, Ca2+, and Mg2+ are essential for physiological processes such as plant growth and cellular homeostasis (Dreyer and Uozumi, 2011). K+ functions as an osmoticum that contributes to cellular turgor adjustment and the control of stomatal opening through the selective movement and redistribution of this cation (Ashley et al, 2006; Szczerba et al, 2009; Dreyer and Uozumi, 2011). Numerous K+ transporter systems related to the uptake and release of K+ from the cell have been reported in various plant species (Baizabal-Aguirre et al, 1999; Szczerba et al, 2009). Shaker-like K+ channels function in stomatal opening and closing through K+ uptake and export in guard cells (Maser et al, 2001; Kim et al, 2015).
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