Soil Bacteria Confer Plant Salt Tolerance by Tissue-Specific Regulation of the Sodium Transporter HKT1

Abstract

Elevated sodium (Na(+)) decreases plant growth and, thereby, agricultural productivity. The ion transporter high-affinity K(+) transporter (HKT)1 controls Na(+) import in roots, yet dysfunction or overexpression of HKT1 fails to increase salt tolerance, raising questions as to HKT1's role in regulating Na(+) homeostasis. Here, we report that tissue-specific regulation of HKT1 by the soil bacterium Bacillus subtilis GB03 confers salt tolerance in Arabidopsis thaliana. Under salt stress (100 mM NaCl), GB03 concurrently down- and upregulates HKT1 expression in roots and shoots, respectively, resulting in lower Na(+) accumulation throughout the plant compared with controls. Consistent with HKT1 participation in GB03-induced salt tolerance, GB03 fails to rescue salt-stressed athkt1 mutants from stunted foliar growth and elevated total Na(+) whereas salt-stressed Na(+) export mutants sos3 show GB03-induced salt tolerance with enhanced shoot and root growth as well as reduced total Na(+). These results demonstrate that tissue-specific regulation of HKT1 is critical for managing Na(+) homeostasis in salt-stressed plants, as well as underscore the breadth and sophistication of plant-microbe interactions.

Do volatile compounds produced by Fusarium oxysporum and Verticillium dahliae affect stress tolerance in plants?

“…In addition, VC-treated plants had increased leaf chlorophyll content (Figure 1(c)) and lateral root density (Figure 1(d)). Similarly, VCs produced by certain PGPR strains also improved plant growth under salt stress (Zhang et al 2008, 2010; Vaishnav et al 2015, 2016; Ledger et al 2016). Decreased leaf surface area and chlorophyll content are common plant responses to salt stress, resulting in reduced photosynthesis and growth (Netondo et al 2004; Hasanuzzaman et al 2013; Negrão et al 2017).…”

“…Bi-partite Petri plate (=I plate), which has been widely used for studying VC-mediated interaction between fungi and plants (Zhang et al 2008; Paul and Park 2013; Bitas et al 2015), was employed for this assessment. One compartment of I plate contained 12 ml half-strength PDA for culturing fungus, and the other compartment had 12 ml Murashige and Skoog (MS) medium (Sigma-Aldrich, St. Louis, MO) supplemented with no NaCl or 100 mM NaCl.…”

“…Chlorophyll content was measured spectrophotometrically as previously described (Hiscox and Israelstam 1979). Leaf surface area was quantified as reported by Zhang et al (2008). Seedlings were photographed using a digital camera (Nikon D80).…”

“…Trichoderma virens and Trichoderma atroviride helped the growth of Arabidopsis thaliana under high NaCl conditions by restoring auxin homeostasis (Contreras-Cornejo et al 2014). Volatile compounds (VCs) produced by some plant growth promoting rhizobacteria (PGPR) have been shown to alleviate plant salt stress (Zhang et al 2008, 2010; Vaishnav et al 2015, 2016; Ledger et al 2016). VCs produced by Bacillus amyloliquefaciens GB03 conferred increased salt tolerance in A. thaliana presumably via tissue-specific regulation of HKT1 , a high-affinity K + transporter, and induced accumulation of osmoprotectants (Zhang et al 2008, 2010).…”

“…Volatile compounds (VCs) produced by some plant growth promoting rhizobacteria (PGPR) have been shown to alleviate plant salt stress (Zhang et al 2008, 2010; Vaishnav et al 2015, 2016; Ledger et al 2016). VCs produced by Bacillus amyloliquefaciens GB03 conferred increased salt tolerance in A. thaliana presumably via tissue-specific regulation of HKT1 , a high-affinity K + transporter, and induced accumulation of osmoprotectants (Zhang et al 2008, 2010). Pseudomonas simiae AU produced VCs that enhanced the growth of soybean seedlings under salt stress, and the underlying mechanism appears to include up-regulation of several salt stress-related proteins (Vaishnav et al 2015).…”