Plant endophytes promote growth and alleviate salt stress in Arabidopsis thaliana

Abstract

Plant growth promoting rhizobacteria (PGPR) are a functionally diverse group of microbes having immense potential as biostimulants and stress alleviators. Their exploitation in agro-ecosystems as an eco-friendly and cost-effective alternative to traditional chemical inputs may positively affect agricultural productivity and environmental sustainability. The present study describes selected rhizobacteria, from a range of origins, having plant growth promoting potential under controlled conditions. A total of 98 isolates (ectophytic or endophytic) from various crop and uncultivated plants were screened, out of which four endophytes (n, L, K and Y) from Phalaris arundinacea , Solanum dulcamara , Scorzoneroides autumnalis , and Glycine max , respectively, were selected in vitro for their vegetative growth stimulating effects on Arabidopsis thaliana Col-0 seedlings with regard to leaf surface area and shoot fresh weight. A 16S rRNA gene sequencing analysis of the strains indicated that these isolates belong to the genera Pseudomonas , Bacillus , Mucilaginibacter and Rhizobium . Strains were then further tested for their effects on abiotic stress alleviation under both Petri-plate and pot conditions. Results from Petri-dish assay indicated strains L, K and Y alleviated salt stress in Arabidopsis seedlings, while strains K and Y conferred increases in fresh weight and leaf area under osmotic stress. Results from subsequent in vivo trials indicated all the isolates, especially strains L, K and Y, distinctly increased A. thaliana growth under both normal and high salinity conditions, as compared to control plants. The activity of antioxidant enzymes (ascorbate peroxidase, catalase and peroxidase), proline content and total antioxidative capacity also differed in the inoculated A. thaliana plants. Furthermore, a study on spatial distribution of the four strains, using either conventional Petri-plate counts or GFP-tagged bacteria, indicated that all four strains were able to colonize the endosphere of A. thaliana root tissue. Thus, the study revealed that the four selected rhizobacteria are good candidates to be explored as plant growth stimulators, which also possess salt stress mitigating property, partially by regulating osmolytes and antioxidant enzymes. Moreover, the study is the first report of Scorzoneroides autumnalis (fall dandelion) and Solanum dulcamara (bittersweet) associated endophytes with PGP effects.

Plant Associated Rhizobacteria for Biocontrol and Plant Growth Enhancement

“…This is an important consideration in biocontrol under field conditions, and as climate change conditions develop. However, if PGPR have coevolved with plants for protracted periods of time, it is likely that they provide more than one benefit to the host plant, and given that the plant provides them with energy (reduced carbon) and niche space, the provide benefit to themselves ( Fan et al, 2020 ).…”

Alleviation of Salinity Stress in Peanut by Application of Endophytic Bacteria

“…and Klebsiella spp. in peanut (Gimenez-Ibanez et al, 2009); and Bacillus sp., Paenibacillus sp., and Pantoea dispersa of peanuts (Li et al, 2019;Fan et al, 2020). Besides these three endophytes (SEN15N, J11N, and REN47N), two other endophytes Bacillus firmus J22N and Bacillus sp.…”

“…Although breeding of tolerant crop varieties is an option, to date there has been limited success in developing such salt-tolerant crop plants (Schubert et al, 2009), necessitated alternate ameliorating or management strategies to achieve sustainable crop growth in soils affected by salinity. The modification in root growth, enhanced uptake of K + concomitantly with a reduction in Na + intake, and up or downregulation of other metabolic processes (Compant et al, 2005;Ryan et al, 2008;Khaliq et al, 2015;Ali et al, 2017;Li et al, 2019;Fan et al, 2020) are also responsible for imparting salinity tolerance. Application of epigallocatechin-3-gallate, salicylic acid, kinetin, silicon, aspirin, Ag-nanoparticals, and spermidine externally have also been found to alleviate abiotic stresses in many plants (Ahammed et al, 2018;Ahanger et al, 2018Ahanger et al, , 2020Hussain et al, 2018;Kaur et al, 2018;Zhang et al, 2018;Alam et al, 2019;Ahmad et al, 2019;Khan et al, 2020).…”

“…Such microbes are also capable of reducing salt stress in plants through the production of ROS scavenging enzymes, modulating osmotic adjustment, enhancing uptake of K to counteract Na, and modulation of signaling pathways, etc. (Sairam and Tyagi, 2004;Compant et al, 2005;Ryan et al, 2008;Fan et al, 2020). Each of the nearly 300000 plant species harbor one or more endophytes that helps them to circumvent many abiotic and biotic stresses (Strobel and Daisy, 2003;Brundrett, 2006).…”

“…inside the root nodules of peanut enhanced yield (Gimenez-Ibanez et al, 2009). Similarly, inoculation of endophytic Bacillus sp., Paenibacillus sp., and Pantoea dispersa obtained from peanut seeds modulated the metabolism of the peanut to modulate growth (Li et al, 2019;Fan et al, 2020). However, very little is known about the role of the endophytic modulation of physiological and biochemical parameters leading to the alleviation of salinity stress in peanuts.…”