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

Abstract

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 photosystems 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.

Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions

“…Understanding naturally occurring PGPR beneficial features and interactions could foster the design of agro-systems with decreased fertilizer inputs and sustained or improved plant yields. The most widely explored plant beneficial trait is the mutual symbiotic biological nitrogen fixation by Rhizobia (Udvardi and Poole 2013), but numerous other nutrient acquisition Subramanian et al 2016 *The role of PGPR SA production in plant defense is debated machineries have been observed which facilitate plant access to macro-nutrients, micro-nutrients, and carbon allocation.…”

“…HMB (Fatima and Anjum 2017). The bacteriocin peptide Thuricin 17 (Th17) from the PGPR Bacillus thuringiensis strain NEB17, has long been known to have antimicrobial activities (Gray et al 2006), but recent proteomic analysis of salt-stress Arabidopsis suggests that it may alleviate the deleterious effect of the abiotic stress on photosystems I and II through upregulation of chloroplast proteins (Subramanian et al 2016).…”

“…Inoculation of Vitis vinifera with Bacillus licheniformis Rt4M10 increased ABA concentrations in leaves (fresh weight) by 76-fold and inoculation with Pseudomonas fluorescens Rt6M10 resulted in ABA increasing by 40-fold; rates of water loss were also reduced in correlation with the increases of ABA in PGPRinoculated V. vinifera (Salomon et al 2014) The products of PGPRs which specifically induce abiotic resistance or tolerance are not as well described in the literature as those known to be involved in defense priming, but likely overlap with those found to promote plant nutrition and biotic resistance. Indeed, reported examples of abiotic resistance elicitors include PGPR products such as ACC deaminase (Glick et al 2007), phytohormones such as IAA (Marulanda et al 2009), signal molecules such as LCOs (Subramanian et al 2016) and AHLs (Ding et al 2016), and BVCs (Liu and Zhang 2015). Promising recent research into the role of PGPR BVCs on Arabidopsis salinity tolerance has shown that the Paraburkholderia phytofirmans P s J N B V C s 2 -u n d e c a n o n e , 7 -h e x a n o l , 3methylbutanol and dimethyl disulfide (DMDS) stimulated positive plant growth under both normal and saline-stress conditions (Ledger et al 2016).…”

“…This approach could allow for a more reliable product that may be readily deployed in response to rapidly changing environmental conditions (Timmusk et al 2017). Rhizosphere bacteria-derived chemicals such as rhizobial NOD factors (lipochito-oligosaccharides or LCOs) have been successfully incorporated into crop protection products, enhancing plant growth in both legumes and non-legumes, as well as stimulating plant defense (Subramanian et al 2016). PGPRs would be an invaluable resource for novel plant defense elicitors which may be more effective than synthetically derived products for crop protection (Bektas and Eulgem 2014;Wiesel et al 2014).…”

Signaling in the phytomicrobiome: breadth and potential

“…These include bacteria in the soil near plant roots, on the surface of plant root systems, in spaces between root cells or inside specialized cells of root nodules; they stimulate plant growth through a wide range of mechanisms ( Gray and Smith, 2005 ; Mabood et al, 2014 ), such as: (1) nutrient solubilization (particularly phosphorus – Boddey et al, 2003 ; Kennedy et al, 2004 ; Trabelsi and Mhamdi, 2013 ), (2) production of metal chelating siderophores, (3) nitrogen fixation ( Vessey, 2003 ; Bhattacharyya and Jha, 2012 ; Drogue et al, 2012 ), (4) production of phytohormones, (5) production of 1-aminocyclopropane-1-carboxylate deaminase, (6) production of volatile organic compounds, (7) induction of systemic resistance [induced systemic resistance (ISR) and systemic required resistance (SAR) – Jung et al, 2008b , 2011 ], and (8) suppression of disease through antibiosis ( Bhattacharyya and Jha, 2012 ; Spence et al, 2014 ). It has also been shown that “signal” compounds produced by bacteria in the phytomicrobiome stimulate plant growth ( Prithiviraj et al, 2003 ; Mabood et al, 2006a ; Lee et al, 2009 ), particularly in the presence of abiotic stress ( Wang et al, 2012 ; Subramanian, 2014 ; Prudent et al, 2015 ). In the broadest sense PGPR include legume-nodulating rhizobia.…”