AUTHOR=Nawaz Muhammad Shoib , Arshad Ayesha , Rajput Lubna , Fatima Kaneez , Ullah Sami , Ahmad Muhammad , Imran Asma 

TITLE=Growth-Stimulatory Effect of Quorum Sensing Signal Molecule N-Acyl-Homoserine Lactone-Producing Multi-Trait Aeromonas spp. on Wheat Genotypes Under Salt Stress

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.553621

DOI=10.3389/fmicb.2020.553621

ISSN=1664-302X

ABSTRACT=<p>Salinity is one of the major threats to agricultural productivity worldwide. Soil and plant management practices, along with inoculation with plant-beneficial bacteria, play a key role in the plant’s tolerance toward salinity stress. The present study demonstrates the potential of acyl homoserine lactone (AHL)-producing plant growth promoting rhizobacteria (PGPR) strains of <italic>Aeromonas</italic> sp., namely, SAL-17 (accession no. <ext-link ext-link-type="DDBJ/EMBL/GenBank" xlink:href="HG763857" xmlns:xlink="http://www.w3.org/1999/xlink">HG763857</ext-link>) and SAL-21 (accession no. <ext-link ext-link-type="DDBJ/EMBL/GenBank" xlink:href="HG763858" xmlns:xlink="http://www.w3.org/1999/xlink">HG763858</ext-link>), for growth promotion of two wheat genotypes inherently different for salt tolerance potential. AHLs are the bacterial signal molecules that regulate the expression of various genes in bacteria and plants. Both <italic>Aeromonas</italic> spp., along with innate plant-growth-promoting (PGP) and salt tolerance traits, showed AHL production which was identified on tandem mass spectrometry as C6-HSL, 3-OH-C5-HSL, 3-OH-C6-HSL, 3-oxo-C7-HSL C10-HSL, 3-oxo-C10-HSL, 3-OH-C10-HSL, 3-oxo-C12-HSL and C6-HSL, and 3-oxo-C10-HSL. The exogenous application of purified AHLs (mix) significantly improved various root parameters at 200 mM NaCl in both salt-sensitive (SSG) and salt-tolerant (STG) genotypes, where the highest increase (≈80%) was observed where a mixture of both strains of AHLs was used. Confocal microscopic observations and root overlay assay revealed a strong root colonization potential of the two strains under salt stress. The inoculation response of both STG and SSG genotypes was evaluated with two AHL-producing strains (SAL-17 and SAL-21) and compared to non-AHL-producing <italic>Aeromonas</italic> sp. SAL-12 (accession no. <ext-link ext-link-type="DDBJ/EMBL/GenBank" xlink:href="HG763856" xmlns:xlink="http://www.w3.org/1999/xlink">HG763856</ext-link>) in saline (EC = 7.63 ms/cm<sup>2</sup>) and non-saline soil. The data reveal that plants inoculated with the bacterial consortium (SAL-21 + SAL-17) showed a maximum increase in leaf proline content, nitrate reductase activity, chlorophyll a/b, stomatal conductance, transpiration rate, root length, shoot length, and grain weight over non-inoculated plants grown in saline soil. Both STG and SSG showed relative effectiveness toward inoculation (percent increase for STG: 165–16%; SSG: 283–14%) and showed a positive correlation of grain yield with proline and nitrate reductase activity. Furthermore, principal component analysis (PCA) and categorical PCA analysis clearly showed an inoculation response in both genotypes, revealing the effectiveness of AHL-producing <italic>Aeromonas</italic> spp. than the non-AHL-producing strain. The present study documents that the consortium of salt-tolerant AHL-producing <italic>Aeromonas</italic> spp. is equally effective for sustaining the growth of STG as well as SSG wheat genotypes in saline soil, but biosafety should be fully ensured before field release.</p>