Lipo-chitooligosaccharide and thuricin 17 act as plant growth promoters and alleviate drought stress in Arabidopsis thaliana

Lipo-chito-oligosaccharide (LCO–from Bradyrhizobium japonicum) and thuricin 17 (Th17–from Bacillus thuringiensis) are bacterial signal compounds from the rhizosphere of soybean that have been shown to enhance plant growth in a range of legumes and non-legumes. In this study, an attempt to quantify phytohormones involved in the initial hours after exposure of Arabidopsis thaliana to these compounds was conducted using UPLC-ESI-MS/MS. A petri-plate assay was conducted to screen for drought stress tolerance to PEG 8000 infusion and plant growth was studied 21-days post-stress. Arabidopsis thaliana plants grown in trays with drought stress imposed by water withhold were used for free proline determination, elemental analysis, and untargeted proteomics using LC-MS/MS studies. At 24 h post-exposure to the signal compounds under optimal growth conditions, Arabidopsis thaliana rosettes varied in their responses to the two signals. While LCO-treated rosettes showed a decrease in total IAA, cytokinins, gibberellins, and jasmonic acid, increases in ABA and SA was very clear. Th17-treated rosettes, on the other hand, showed an increase in IAA and SA. Both treatments resulted in decreased JA levels. Under severe drought stress imposed by PEG 8000 infusion, LCO and Th17 treatments were found to significantly increase fresh and dry weight over drought-stressed control plates, indicating that the presence of the signaling compounds decreased the negative effects experienced by the plants. Free proline content increased in LCO- and Th17-treated plants after water-withhold drought stress. Elemental analysis showed a significant increase in carbon percentage at the lower concentration of Th17. Untargeted proteomics revealed changes in the levels of drought-specific ribosomal proteins, glutathione S-transferase, late embryogenesis proteins, vegetative storage proteins 1 and 2, thaumatin-like proteins, and those related to chloroplast and carbon metabolism. The roles of some of these significantly affected proteins detected under drought stress are discussed

Proteomic Studies on the Effects of Lipo-Chitooligosaccharide and Thuricin 17 under Unstressed and Salt Stressed Conditions in Arabidopsis thaliana

Plants, being sessile organisms, are exposed to widely varying environmental conditions throughout their life cycle. Compatible plant-microbe interactions favor plant growth and development, and help plants deal with these environmental challenges. Microorganisms produce a diverse range of elicitor molecules to establish symbiotic relationships with the plants they associate with, in a given ecological niche. Lipo-chitooligosaccharide (LCO) and thuricin 17 (Th17) are two such compounds shown to positively influence plant growth of both legumes and non-legumes. Arabidopsis thaliana responded positively to treatment with the bacterial signal compounds LCO and Th17 in the presence of salt stress (up to 250 mM NaCl). Shotgun proteomics of unstressed and 250 mM NaCl stressed A. thaliana rosettes (7 days post stress) in combination with the LCO and Th17 revealed many known, putative, hypothetical and unknown proteins. Overall, carbon and energy metabolic pathways were affected under both unstressed and salt stressed conditions when treated with these signals. PEP carboxylase, Rubisco-oxygenase large subunit, pyruvate kinase, and proteins of photosystem I and II were some of the noteworthy proteins enhanced by the signals, along with other stress related proteins. These findings suggest that the proteome of A. thaliana rosettes is altered by the bacterial signals tested, and more so under salt stress, thereby imparting a positive effect on plant growth under high salt stress. The roles of the identified proteins are discussed here in relation to salt stress adaptation, which, when translated to field grown crops can be a crucial component and of significant importance in agriculture and global food production. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD004742

A Proteomic Approach to Lipo-Chitooligosaccharide and Thuricin 17 Effects on Soybean GerminationUnstressed and Salt Stress

<div><p>Salt stress is an important abiotic stressor affecting crop growth and productivity. Of the 20 percent of the terrestrial earth’s surface available as agricultural land, 50 percent is estimated by the United Nations Environment Program to be salinized to the level that crops growing on it will be salt-stressed. Increased soil salinity has profound effects on seed germination and germinating seedlings as they are frequently confronted with much higher salinities than vigorously growing plants, because germination usually occurs in surface soils, the site of greatest soluble salt accumulation. The growth of soybean exposed to 40 mM NaCl is negatively affected, while an exposure to 80 mM NaCl is often lethal. When treated with the bacterial signal compounds lipo-chitooligosaccharide (LCO) and thuricin 17 (Th17), soybean seeds (variety Absolute RR) responded positively at salt stress of up to 150 mM NaCl. Shotgun proteomics of unstressed and 100 mM NaCl stressed seeds (48 h) in combination with the LCO and Th17 revealed many known, predicted, hypothetical and unknown proteins. In all, carbon, nitrogen and energy metabolic pathways were affected under both unstressed and salt stressed conditions when treated with signals. PEP carboxylase, Rubisco oxygenase large subunit, pyruvate kinase, and isocitrate lyase were some of the noteworthy proteins enhanced by the signals, along with antioxidant glutathione-S-transferase and other stress related proteins. These findings suggest that the germinating seeds alter their proteome based on bacterial signals and on stress, the specificity of this response plays a crucial role in organ maturation and transition from one stage to another in the plants' life cycle; understanding this response is of fundamental importance in agriculture and, as a result, global food security. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD004106.</p></div

Soybean is less impacted by water stress using Bradyrhizobium japonicum and thuricin-17 from Bacillus thuringiensis

International audienceClimate change is forecasted to induce more drought stress events. Water scarcity is already the most limiting abiotic stress for crop production. With higher food demand, there is a need for sustainable solutions to cope with the loss of productivity due to water stress. It is known that plant growth-promoting rhizobacteria (PGPR) can colonize plant roots and increase plant growth. However, there is actually no sustainable method to decrease the impact of water stress. Therefore, we hypothesized that an application of thuricin-17, a molecule produced by the PGPR Bacillus thuringiensis, could enhance soybean tolerance to water stress. We grew soybean plants for 1 month in growth chambers in order to evaluate their response to thuricin-17 root application under drought, in association with the inoculation of N2-fixing Bradyrhizobium japonicum. We measured traits reflecting root architecture: number of tips, root diameter, root length, number of nodules; water fluxes: water potential, stomatal conductance; carbon nutrition: leaf area, photosynthetic rate, biomass and carbon partitioning; nitrogen nutrition: nitrogen partitioning and hormone signalling: abscisic acid concentration during the vegetative growth period. Our results show that thuricin-17 application under water stress increased plant biomass by 17 %, thus masking drought impact. This effect is due to modifications of below-ground structures, with 37 % increase of root and 55 % increase of nodule biomass, and to slight increases of leaf area and photosynthetic rate. We also observed that application of thuricin-17 induced a 30 % increase of root abscisic acid, an increase of root length and of leaf water potential. Finally, thuricin-17 induced an activation of nodule formation by 40 %, a partial restoration of nodule-specific activity, nodule growth and consequently, an increase by 17 % of the total nitrogen amount in the plant. Overall, our findings reveal a new method to decrease the negative impact of water stress. Results also demonstrate that the plant restored an adequate water and N balance by changing its root structure

Elemental analysis of soybean seeds after 48 h from the onset of germination.

<p>Panels A, B, C represent data for unstressed treatments and Panels D, E, F represent data for stressed treatments.</p

Total number of proteins identified at 99% protein probability and total spectra at 95% peptide probability, with 2 minimum peptides.

<p>Total number of proteins identified at 99% protein probability and total spectra at 95% peptide probability, with 2 minimum peptides.</p

Enzyme code distribution categorized based on main enzyme classes in unstressed and salt stressed treatments.

<p>Enzyme code distribution categorized based on main enzyme classes in unstressed and salt stressed treatments.</p

Soybean seed germination 48 h post treatment (un-stressed—Panel A; 100 mM NaCl stress—Panel B).

<p>Soybean seed germination 48 h post treatment (un-stressed—Panel A; 100 mM NaCl stress—Panel B).</p