Changes in Root Exudates and Root Proteins in Groundnut–Pseudomonas sp. Interaction Contribute to Root Colonization by Bacteria and Defense Response of the Host
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Selection and application of rhizobacteria, for improved plant health will benefit from a complete understanding of the plant–bacteria interaction. Root exudates (REs) are known to contain signal molecules that facilitate beneficial association of plants with microbes. We have selected a tentatively identified Pseudomonas sp. (RP2), from 126 groundnut (Arachis hypogaea L.)-associated bacterial isolates that significantly promoted growth of groundnut and also induced resistance against the stem rot pathogen Sclerotium rolfsii. REs were collected from 12 to 24 days grown RP2-bacterized and non-bacterized plants and analyzed through gas chromatography coupled with mass spectrometer. Several organic acids, fatty acids, sugars, hydrocarbons, and alcohols were detected. In the untargeted multivariate analysis of the REs, relative content of eight compounds varied significantly on RP2 bacterization. Among these eight compounds, myristic acid, stearic acid, and palmitic acid, positively influenced the root colonization by RP2. Benzoic acid and salicylic acid, increased in RP2-bacterized REs, showed the highest growth inhibition of S. rolfsii. In root proteomics, 11 differentially expressed proteins were identified by 2D-gel electrophoresis followed by matrix-assisted laser desorption ionization-time of flight. Chitinase, thaumatin-like protein, ascorbate peroxidase, and glutathione S-transferase, known to have a role in plant defense against phytopathogens, were upregulated in RP2 interaction. Similarly, upregulation of enolase in roots is likely to improve plant growth in RP2-bacterized groundnut. We conclude that colonization of groundnut roots by RP2 resulted in exudation of metabolites that facilitated root colonization, suppressed fungal growth, promoted plant growth, and also increased the expression of defense-related proteins in the roots.
KeywordsGroundnut Pseudomonas sp. PGPR Root exudates Root proteins Antifungal
We thank Department of Biotechnology (DBT), Government of India (GoI) for financial support under project No: BT/PR4175/AGR/21/350/2011 dated 01.03.2012. SA thanks Council of Scientific and Industrial Research, GoI for Senior research fellowship. TSR acknowledges financial support from Dr. D. S. Kothari postdoctoral fellowship scheme (BSR/BL/16-17/0344). We also thank the Department of Science and Technology (DST), GoI, Funds for Infrastructure in Science and Technology, Level II support (DST-FIST level II), and Special Assistance Programme-UGC (SAP-UGC) to the Department of Plant Sciences, School of Life Sciences. The authors are grateful to Groundnut division, International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, for providing Arachis hypogaea L. seeds and Dr. Vincent Vadez, Principal Scientist, Division of Crop Physiology, ICRISAT, Hyderabad, for allowing the use of WinRHIZO Pro 5.0 root analyzer facility.
ARP designed the experiment. SA isolated and screened groundnut PGPR, and analyzed REs by GC-MS. TSR carried out root proteomics using 2DE. ARP, SA, and TSR analyzed the data and wrote the manuscript.
Compliance with Ethical Standards
Conflict of interest
The authors declare no conflict of interest.
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