Pseudomonas spp. Mediate defense response in sugarcane through differential exudation of root phenolics

Faluk Shair; Humaira Yasmin; Muhammad Nadeem Hassan; Othman M Alzahrani; Ahmed Noureldeen

doi:10.1016/j.sjbs.2021.09.030

Pseudomonas spp. Mediate defense response in sugarcane through differential exudation of root phenolics

Saudi J Biol Sci. 2021 Dec;28(12):7528-7538. doi: 10.1016/j.sjbs.2021.09.030. Epub 2021 Sep 20.

Authors

Faluk Shair¹, Humaira Yasmin¹, Muhammad Nadeem Hassan¹, Othman M Alzahrani², Ahmed Noureldeen²

Affiliations

¹ Department of Biosciences, COMSATS University Islamabad (CUI), Islamabad, Park road, Chakshazad 44000, Islamabad, Pakistan.
² Department of Biology, College of Sciences, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia.

Abstract

Pseudomonas spp., a ubiquitous biocontrol agent, protects the plants from phytopathogens by suppressing them directly by reinforcing the plant's intrinsic defense mechanism. Root exudated phenolics play an important role in establishing the rhizobacteria population and cross the host boundaries in beneficial plant-microbe interaction. In this study, Pseudomonas spp. HU-8 & HU-9 antagonized the sugarcane red rot pathogen (C. falcatum) and showed a positive chemotactic response against different concentrations (10-30 µM) of synthetic phenolic acids like p-coumaric, vanillic, and 3,4 di-hydroxybenzoic acid. In a pot experiment, they effectively colonized the sugarcane rhizosphere and mediated defense response in sugarcane plants challenged with red rot pathogen C. falcatum by regulating the exudation of root phenolics under hydroponic conditions. They significantly induced the activity of the antioxidant enzymes CAT (1.24-1.64 fold), PO (0.78-1.61 fold), PAL (0.77-0.97 fold), and PPO (3.67-3.73 fold) over untreated plants in sugarcane. They also induced the total phenolic contents (TPC) in sugarcane in the presence (6.56-10.29 mg/g GAE) and absence (2.89-4.16 mg/g GAE) of the pathogen quantified through the Folin-Ciocalteu (FC) method. However, their effect was lower than that of the pathogen (4.34-8 mg/g GAE). The Pseudomonas spp. significantly colonized the sugarcane rhizosphere by maintaining a cell population of (1.0E + 07-1.3E + 08 CFU/mL). A significant positive Pearson's correlation was observed between the root exudated total phenolic contents, antioxidant enzymatic activities, and rhizospheric population of inoculated bacteria. The 16S rRNA and rpoD gene analysis showed sequence conservation (C: 0.707), average number of nucleotide differences (k: 199.816), nucleotide diversity, (Pi): 0.09819), average number of informative nucleotide sites per site (Psi: 0.01275), GC content (0.57), and polymorphic sites (n = 656). These diverse Pseudomonas spp. could be an ideal bio-inoculants for a broad range of hosts especially graminaceous crops.

Keywords: Defense response; Differential exudation; Pseudomonas spp.; Sugarcane; Total phenolics compounds.