Choline and Osmotic-Stress Tolerance Induced in Arabidopsis by the Soil Microbe Bacillus subtilis (GB03)

Abstract

Choline (Cho) is an essential nutrient for humans as well as the precursor of glycine betaine (GlyBet), an important compatible solute in eukaryotes that protects cells from osmotic stress caused by dehydrating conditions. The key enzyme for plant Cho synthesis is phosphoethanolamine N-methyltransferase (PEAMT), which catalyzes all three methylation steps, including the rate-limiting N-methylation of phosphoethanolamine. Herein, we report that the beneficial soil bacterium Bacillus subtilis (strain GB03) enhances Arabidopsis Cho and GlyBet synthesis associated with enhanced plant tolerance to osmotic stress. When stressed with 100 mM exogenous mannitol, GB03-exposed plants exhibit increased transcript level of PEAMT compared with stressed plants without bacterial exposure. Endogenous Cho and GlyBet metabolite pools were elevated by more than two- and fivefold, respectively, by GB03 treatment, consistent with increased stress tolerance. Moreover, in the xipotl mutant line with reduced Cho production, a loss of GB03-induced drought tolerance is observed. Osmotic-stressed plants with or without GB03 exposure show similar levels of abscsisic acid (ABA) accumulation in both shoots and roots, suggesting that GB03-induced osmoprotection is ABA independent. GB03 treatment also improves drought tolerance in soil-grown plants as characterized by phenotypic comparisons, supported by an elevated accumulation of osmoprotectants. These results provide a biological strategy to enhance Cho biosynthesis in plants and, in turn, increase plant tolerance to osmotic stress by elevating osmoprotectant accumulation.

Understanding and Enhancing Soil Biological Health: The Solution for Reversing Soil Degradation

“…With emerging extreme climatic changes, another critical question is whether cropping system sustainability can be increased by using plants that can interact with a variety of PGPR/B that are capable of increasing photosynthetic capacity [126,127], conferring drought and salt tolerance [126,[128][129][130], and improving the effectiveness of the plant's own iron acquisition mechanisms [129]. A variety of companies have begun to offer new products that consist of PGPR/B inoculants (soil and/or seed treatments), or chemicals aimed at increasing root exudation to help foster PGPR/B establishment.…”

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).…”

“…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).…”

Bioremediation Potential Assessment of Plant Growth-Promoting Autochthonous Bacteria: a Lignite Mine Case Study

“…We acknowledge that soil-assisted strategies are not always economically feasible and complicate infrastructure. Thus we are further exploring the potential roles of other previously reported PGP Bacillus spp., such as B. subtilis [40], B. amyloliquefaciens [41], B. pumilus [10], B. licheniformis [42], and B. megaterium [43], plus other autochthonous bacterial species, alone or together with re-vegetation, in bioremediation of lignite mine waste.…”