Rice Na+-Permeable Transporter OsHAK12 Mediates Shoots Na+ Exclusion in Response to Salt Stress

Linan Zhang,Xuan Luo,Shaowen Song,Dandan Mao,Sheng Luan,Xiaohui Wang,Liangbi Chen,Yanfang Li,Yan Chen,Xiangyu Sun

doi:10.3389/fpls.2021.771746

Abstract

Soil salinity has become a major stress factor that reduces crop productivity worldwide. Sodium (Na+) toxicity in a number of crop plants is tightly linked with shoot Na+ overaccumulation, thus Na+ exclusion from shoot is crucial for salt tolerance in crops. In this study, we identified a member of the high-affinity K+ transport family (HAK), OsHAK12, which mediates shoots Na+ exclusion in response to salt stress in rice. The Oshak12 mutants showed sensitivity to salt toxicity and accumulated more Na+ in the xylem sap, leading to excessive Na+ in the shoots and less Na+ in the roots. Unlike typical HAK family transporters that transport K+, OsHAK12 is a Na+-permeable plasma membrane transporter. In addition, OsHAK12 was strongly expressed in the root vascular tissues and induced by salt stress. These findings indicate that OsHAK12 mediates Na+ exclusion from shoot, possibly by retrieving Na+ from xylem vessel thereby reducing Na+ content in the shoots. These findings provide a unique function of a rice HAK family member and provide a potential target gene for improving salt tolerance of rice.

Highlights

Soil salinity represents a primary hazard to crop productivity (Munns and Tester, 2008; Ismail and Horie, 2017; Munns et al, 2020)
We identified a member of the high-affinity K+ transport family (HAK), OsHAK12, which mediates shoots Na+ exclusion in response to salt stress in rice
Considering its expression pattern and subcellular localization, its disruption was responsible for the hypersensitivity to salinity stress and functions in Na+ retrieving from the xylem vessels (Figures 1–3, 5A), we suggest that OsHAK12, may be as a Na+-permeable transporter mediating Na+ transport in rice roots

Summary

Introduction

Soil salinity represents a primary hazard to crop productivity (Munns and Tester, 2008; Ismail and Horie, 2017; Munns et al, 2020). The rice salt-tolerant QTL SKC1/OsHKT1;5, the wheat salt-tolerant QTLs Nax1/TmHKT1;4 and Nax2/TmHKT1;5, and the maize salt-tolerant QTL ZmNC1/ZmHKT1 all encode HKT-type Na+ transporters that function to Arabidopsis HKT1 (Ren et al, 2005; Huang et al, 2006; Byrt et al, 2007; Munns et al, 2012; Zhang et al, 2018) These studies have showed that Na+- permeable HKT1 transporters mediate Na+ retrieving from xylem vessels and beneficial for enhancement of salt tolerance. Apart from HKT1 family transporters, it remains largely unknown if other types transporters are involved in retrieving Na+ from xylem vessels

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Conclusion