Rhizospheric Bacillus amyloliquefaciens Protects Capsicum annuum cv. Geumsugangsan From Multiple Abiotic Stresses via Multifarious Plant Growth-Promoting Attributes.

Elham Ahmed Kazerooni,In-Jung Lee,Arjun Adhikari,Sang-Mo Kang,Abdullah Mohammed Al-Sadi,Lee-Rang Kim,Sajeewa S N Maharachchikumbura

doi:10.3389/fpls.2021.669693

Abstract

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that can be utilized to improve plant responses against biotic and abiotic stresses. In this study, we investigated whether PGPR (Bacillus amyloliquefaciens) isolated from the endorhizosphere of Sasamorpha borealis have the potential to sustain pepper growth under drought, salinity, and heavy metal stresses. The bacterial strain was determined based on 16S rDNA and gyrB gene sequencing and characterized based on the following biochemical traits: nitrogen fixation; 1-aminocyclopropane-1-carboxylate deaminase activity; indole acetic acid production; inorganic phosphate, potassium, zinc, and silicon solubilization; and siderophore production. Various abiotic stresses were applied to 28-day-old pepper seedlings, and the influence of the PGPR strain on pepper seedling growth under these stress conditions was evaluated. The application of PGPR improved survival of the inoculated pepper plants under stress conditions, which was reflected by higher seedling growth rate and improved physiochemical traits. The PGPR-treated plants maintained high chlorophyll, salicylic acid, sugar, amino acid, and proline contents and showed low lipid metabolism, abscisic acid, protein, hydrogen peroxide contents, and antioxidant activities under stress conditions. Gene expression studies confirmed our physiological and biochemical findings. PGPR inoculation led to enhanced expression of XTH genes and reduced expression of WRKY2, BI-1, PTI1, and binding immunoglobulin protein (BiP) genes. We conclude that the PGPR strain described in this study has great potential for use in the phytoremediation of heavy metals and for enhancing pepper plant productivity under stress conditions, particularly those involving salinity and drought.

Highlights

Plants are detrimentally affected by multiple environmental stimuli in the form of various abiotic and biotic stresses
The 16S rDNA and gyrB gene sequencing and phylogenetic analysis disclosed that the selected Plant growth-promoting rhizobacteria (PGPR) strain (B11) had a 100% similarity with the known sequences in GenBank and belonged to Bacillus amyloliquefaciens
Our results show that PGPR application ameliorates the expression of Xyloglucan endotransglucosylase/hydrolases (XTHs) (CaXTH1 and CaXTH2) and improves abiotic stress tolerance in pepper seedlings

Summary

Introduction

Plants are detrimentally affected by multiple environmental stimuli in the form of various abiotic and biotic stresses. Water deficiency and salinity are the prevalent environmental restraints that affect the morphological, physiological, biochemical, and molecular responses of plants and cause enormous losses in agriculture (Jaleel et al, 2007; Khan et al, 2019). Soil pollution is prevalent in different places. It is affected by industrial processes, cultivation practices, and human activities. These processes can lead to the spread of, for example, heavy metals, which can create severe ecological problems even at low levels (Wuana and Okieimen, 2011). There are other abiotic stresses that are more location specific, including frost (Keep et al, 2021; Simioniuc et al, 2021), ultraviolet radiation (Böttner et al, 2021; Navarro et al, 2021), and floods (Khan et al, 2020; Liu et al, 2021)

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Conclusion