Chloride-Transporting OsHKT1;1 Splice Variants and Their Expression Profiles Under Salinity Stress in Rice.

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• The high-affinity K+ transporter (HKT) family, including OsHKT1;1, is crucial for maintaining sodium (Na+) homeostasis and salinity tolerance in rice.
• Previous research identified multiple OsHKT1;1 splicing variants, but their transport functions remain largely uncharacterized, with most studies focusing on the full-length (FL) protein.

Purpose of the Study:

• To investigate and compare the function and gene expression of the OsHKT1;1-V2 splice variant with the full-length OsHKT1;1 (OsHKT1;1-FL).
• To elucidate the ion transport properties and subcellular localization of OsHKT1;1-V2.

Main Methods:

• Two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes.
• Subcellular localization studies in oocytes and Arabidopsis mesophyll cells.
• Functional assays using a yeast mutant.
• Quantitative PCR (qPCR) for gene expression analysis.

Main Results:

• OsHKT1;1-V2 demonstrated functional bidirectional currents and primarily mediated chloride (Cl-) transport with weak Na+ selectivity, contrasting with the Na+-selective OsHKT1;1-FL.
• Oocytes expressing OsHKT1;1-V2 showed higher Cl- accumulation, and yeast assays confirmed OsHKT1;1-FL mediates Na+ uptake, while OsHKT1;1-V2 does not.
• Subcellular localization revealed plasma membrane localization for both OsHKT1;1-V2 and OsHKT1;1-FL in oocytes and Arabidopsis.
• Quantitative PCR showed higher OsHKT1;1-FL transcript abundance in Nipponbare and lower OsHKT1;1-V2 levels in Pokkali under salt stress.

Conclusions:

• OsHKT1;1-V2 possesses distinct ion transport properties, primarily facilitating Cl- transport, which differs significantly from the Na+ transport function of OsHKT1;1-FL.
• The differential expression patterns of OsHKT1;1 variants in rice cultivars under salt stress suggest complex regulatory mechanisms for ion homeostasis.
• This study expands our understanding of HKT transporter diversity and their roles in plant salinity tolerance.