The outward shaker channel OsK5.2 improves plant salt tolerance by contributing to control of both leaf transpiration and K⁺ secretion into xylem sap

Abstract

Soil salinity constitutes a major environmental constraint to crop production worldwide. Leaf K + /Na + homoeostasis, which involves regulation of transpiration, and thus of the xylem sap flow, and control of the ionic composition of the ascending sap, is a key determinant of plant salt tolerance. Here, we show, using a reverse genetics approach, that the outwardly rectifying K + -selective channel OsK5.2, which is involved in both K + release from guard cells for stomatal closure in leaves and K + secretion into the xylem sap in roots, is a strong determinant of rice salt tolerance (plant biomass production and shoot phenotype under saline constraint). OsK5.2 expression was upregulated in shoots from the onset of the saline treatment, and OsK5.2 activity in guard cells led to a fast decrease in transpirational water flow and, therefore, reduced Na + translocation to shoots. In roots, upon saline treatment, OsK5.2 activity in xylem sap K + loading was maintained, and even transiently increased, outperforming the negative effect on K + translocation to shoots resulting from the reduction in xylem sap flow. Thus, the overall activity of OsK5.2 in shoots and roots, which both reduces Na + translocation to shoots and benefits shoot K + nutrition, strongly contributes to leaf K + /Na + homoeostasis.

Genome-wide identification of Shaker K+ channel family in Nicotiana tabacum and functional analysis of NtSKOR1B in response to salt stress

“…The rice Shaker outward rectifier potassium channel homolog gene OsK5.2 regulates stomatal closure in leaf guard cells, reducing water transpiration and Na + transport to leaves, and enhances K + secretion into the xylem sap in roots, thus maintaining and enhancing K + transport under salt stress conditions. The OsK5.2 knockout mutant exhibited increased sensitivity to salt stress, further affirming OsK5.2 ’s critical role in regulating rice salt tolerance ( Zhou et al., 2022 ). Previous research has indicated that Shaker potassium channels are involved in salt stress response through their impact on K + /Na + balance.…”

“…Furthermore, OsK5.2’s presence in guard cells amplifies K + efflux under salt stress, leading to stomatal closure, diminished water loss, and reduced salt buildup, which in turn decreases Na + transport to leaves( Nguyen et al., 2017 ). In summary, this potassium channel positively influences plant salt tolerance by ensuring a superior K + /Na + balance( Zhou et al., 2022 ). The NtSKOR1B outward potassium channel, part of the tobacco Shaker family, is located in the root cortex and leaf vascular bundles.…”

Rice potassium transporter OsHAK18 mediates phloem K+ loading and redistribution

“…In addition, OsHAK21 localized at passage cells in endodermis ( En ) may also contribute to K + uptake under salt stress. The outward K + channel OsK5.2 mediates K + secretion into xylem sap (Nguyen et al., 2017; Zhou et al., 2022). K + in the xylem is translocated to shoots with a transpiration stream.…”

Arbuscular mycorrhizal fungusRhizophagus irregularisexpresses an outwardly Shaker-like channel involved in rice potassium nutrition

“…The collected shoots were weighed to determine their dry weight (DW). Ions were extracted from the tissues in 0.1 N HCl for 3 days and assayed by flame spectrophotometry (SpectrAA 220FS, Varian) (48).…”