Plant salt-tolerance mechanisms

Abstract

Crop performance is severely affected by high salt concentrations in soils. To engineer more salt-tolerant plants it is crucial to unravel the key components of the plant salt-tolerance network. Here we review our understanding of the core salt-tolerance mechanisms in plants. Recent studies have shown that stress sensing and signaling components can play important roles in regulating the plant salinity stress response. We also review key Na+ transport and detoxification pathways and the impact of epigenetic chromatin modifications on salinity tolerance. In addition, we discuss the progress that has been made towards engineering salt tolerance in crops, including marker-assisted selection and gene stacking techniques. We also identify key open questions that remain to be addressed in the future.

Keywords: NaCl; abiotic stress; biotechnology; engineering of salt-tolerant plants; plant salinity tolerance.

Figure 1

Overview of cellular Na⁺ transport mechanisms and important components of the salt stress response network in plant root cells. Na⁺ (depicted in red) enters the cell via non- selective cation channels (NSCCs) and other, as yet largely unknown membrane transporters (cellular Na⁺ influx mechanisms highlighted with orange). Inside the cell, Na⁺ is sensed by an as yet unidentified sensory mechanism. At the next step, Ca²⁺, ROS and hormone signaling cascades are activated. CBLs, CIPKs and CDPKs are part of the Ca²⁺ signaling pathway (sensing and signaling components highlighted with blue), which can alter the global transcriptional profile of the plant (transcription factor families in the nucleus depicted in purple; an AP2/ERF and a bZIP transcription factor that negatively regulate HKT gene expression are shown as an example). Ultimately these early signaling pathways result in expression and activation of cellular detoxification mechanisms, including HKT, NHX and the SOS Na⁺ transport mechanisms as well as osmotic protection strategies (cellular detoxification mechanisms highlighted with light green). Furthermore, the Na⁺ distribution in the plant is regulated in a tissue-specific manner by unloading of Na⁺ from the xylem.