Burkholderia phytofirmans PsJN induces long-term metabolic and transcriptional changes involved in Arabidopsis thaliana salt tolerance

Abstract

Salinity is one of the major limitations for food production worldwide. Improvement of plant salt-stress tolerance using plant-growth promoting rhizobacteria (PGPR) has arisen as a promising strategy to help overcome this limitation. However, the molecular and biochemical mechanisms controlling PGPR/plant interactions under salt-stress remain unclear. The main objective of this study was to obtain new insights into the mechanisms underlying salt-stress tolerance enhancement in the salt-sensitive Arabidopsis thaliana Col-0 plants, when inoculated with the well-known PGPR strain Burkholderia phytofirmans PsJN. To tackle this, different life history traits, together with the spatiotemporal accumulation patterns for key metabolites and salt-stress related transcripts, were analyzed in inoculated plants under short and long-term salt-stress. Inoculated plants displayed faster recovery and increased tolerance after sustained salt-stress. PsJN treatment accelerated the accumulation of proline and transcription of genes related to abscisic acid signaling (Relative to Dessication, RD29A and RD29B), ROS scavenging (Ascorbate Peroxidase 2), and detoxification (Glyoxalase I 7), and down-regulated the expression of Lipoxygenase 2 (related to jasmonic acid biosynthesis). Among the general transcriptional effects of this bacterium, the expression pattern of important ion-homeostasis related genes was altered after short and long-term stress (Arabidopsis K+ Transporter 1, High-Affinity K+ Transporter 1, Sodium Hydrogen Exchanger 2, and Arabidopsis Salt Overly Sensitive 1). In all, the faster and stronger molecular changes induced by the inoculation suggest a PsJN-priming effect, which may explain the observed tolerance after short-term and sustained salt-stress in plants. This study provides novel information about possible mechanisms involved in salt-stress tolerance induced by PGPR in plants, showing that certain changes are maintained over time. This opens up new venues to study these relevant biological associations, as well as new approaches to a better understanding of the spatiotemporal mechanisms involved in stress tolerance in plants.

Volatile-Mediated Effects Predominate in Paraburkholderia phytofirmans Growth Promotion and Salt Stress Tolerance of Arabidopsis thaliana

“…Previous results from our group suggest that early PsJN inoculation is sufficient to enhance tolerance to salinity in A. thaliana , rather than just increasing growth rate regardless of saline stress (Pinedo et al, 2015). However, an estimation of salinity-induced mortality, senescence and tissue damage is necessary to ascertain if sodium exclusion or tissue tolerance mechanisms are being activated in the plants (Roy et al, 2014), and to determine if salt toxicity is effectively reduced by bacterial inoculation.…”

“…Consequently, mutant strains of P. phytofirmans in colonization related functions were also included in the analysis, in order to test their influence on PsJN-mediated salinity tolerance in A. thaliana . When PsJN- BpI.1 inoculated plants were challenged with 150/15 mM NaCl/CaCl 2 , a concentration producing the highest differences among wild type PsJN inoculated and N. I. salt stressed plants (Pinedo et al, 2015), the effect of the mutant displayed no significant differences to that of the wild type strain ( Figure 1B ). Finally, a mutant was produced with an inactivated version of gene FliA , which encodes for a main regulator protein controlling flagellar assembly, to investigate if flagella can work out as bacterial elicitors of IST in A. thaliana .…”

“…Bacterial determinants of growth promotion and salinity tolerance in A. thaliana in response to PsJN inoculation have been studied in this work, based on previous results showing that short- and long-term changes in the response of inoculated plants are able to enhance their growth in the presence of salt (Pinedo et al, 2015). Here, we have explored the onset of salinity tolerance conferred by P. phytofirmans , and the extent of long-term induction of plant growth and stress-survival by inoculation of strain PsJN, quantifying germination, growth parameters, sodium accumulation and water management in inoculated A. thaliana plants exposed to increasing concentrations of salt in irrigation water, and comparing these to N. I. control plants.…”

“…Over the last few years, several studies have reported the ability of isolated microorganisms to induce plant tolerance to salinity once they have been inoculated to seeds or young plantlets (reviewed in Yang et al, 2009; Dodd and Pérez-Alfocea, 2012; Shrivastava and Kumar, 2015), including a variety of hosts, like wheat (Nadeem et al, 2013; Singh et al, 2015), maize (Hamdia et al, 2004; Nadeem et al, 2009), cotton (Liu et al, 2013; Egamberdieva et al, 2015), tomato (Mayak et al, 2004; Ali et al, 2014), lettuce (Barassi et al, 2006; Kohler et al, 2009), sunflower (Shilev et al, 2010; Tewari and Arora, 2014) and Arabidopsis (Zhang et al, 2008; Kim et al, 2014; Sukweenadhi et al, 2015). Among the PGPR that have been demonstrated to play a role in salt stress tolerance induction, a wide diversity of bacteria is included, encompassing several members of the γ-proteobacteria class, specially within the genus Pseudomonas (Ahmad et al, 2013; Nadeem et al, 2013; Chang et al, 2014; Han et al, 2015), α-proteobacteria belonging to the Azospirillum genus (del Amor and Cuadra-Crespo, 2011; Nia et al, 2012; Sahoo et al, 2014), and β-proteobacteria like Achromobacter (Mayak et al, 2004) or Paraburkholderia (Talbi et al, 2013; Pinedo et al, 2015). Several examples have also been described for the phylum Firmicutes, with special emphasis on the genus Bacillus (Zhang et al, 2008; Kohler et al, 2009; Karlidag et al, 2013; Ramadoss et al, 2013; Han et al, 2015), and also some examples have been described within the Actinobacteria phylum (Sadeghi et al, 2012; Palaniyandi et al, 2014; Gond et al, 2015).…”

“…We have recently described the ability of P. phytofirmans PsJN to enhance salt tolerance of A. thaliana , focusing on metabolic and transcriptional changes in the plant, related to stress-perception and stress-responsive pathways (Pinedo et al, 2015). That study showed that PsJN inoculation increased tolerance to salt treatment in short and long-term exposure, suggesting a priming (IST) effect mediated by bacterial inoculation, which involves modulation of the transcriptional response of the plant in the presence of stress.…”