TaTAR2s and SAUR36 Genes Play a Role in Improving the Growth of Wheat Seedlings by Rhizobacteria

The aim of this study was to isolate Bacillus strains from the rhizospheric environment and examine their impact on the growth of wheat seedlings and key genes related to indole-3-acetic acid (IAA) synthesis. After the soil was taken to the lab and exposed to heat treatment, the rhizobacteria were isolated as individual colonies, then grown with or without tryptophan and tested with Salkowski’s reagent. The best IAA-producing strains, along with Bacillus amyloliquefaciens FZB42, were used at three different concentrations in two ways: (i) bacterial cells with their culture medium (BWM) and (ii) bacterial cells without culture medium (BWoM). Various morphological traits, as well as pigment content, were measured. Finally, the expression of three IAA-related genes in the leaves of wheat seedlings treated with the best strain was measured via quantitative real–time PCR (qRT‒PCR). The highest IAA production occurred in the presence of tryptophan, with levels ranging from 61.84 to 95.89 µg/ml for 8 Bacillus strains. Although these strains had beneficial impacts on growth and pigment traits when used as BWM, some of them had negative effects at certain concentrations. However, when the strains were used as BWoM, they consistently had greater effects on the characteristics of the shoots and roots. The best strain was identified as B. cereus through 16 S ribosomal DNA (rDNA) analysis. The genes studied showed reduced expression in leaves inoculated with the C6 strain through both BWM and BWoM. Using these rhizobacterial strains as BWoM has the potential to offer a sustainable and eco-friendly approach to enhance crop productivity.