ABA analogue produced by Bacillus marisflavi modulates the physiological response of host-plant under drought stress

Present study aims to understand the molecular mechanism involved in beneficial rhizobacteria mediated alleviation of drought stress in host plant. Bacillus marisflavi CRDT-EB-1 isolated from the rhizosphere soil was found effective in inducing resistance against drought stress in mustard seedlings. Among the different bacterial derivatives tested, the culture filtrate was found to contain bioactive molecules. Solvent extract of bacterial culture filtrate yielded seven distinct bands/ fractions on thin layer chromatography (TLC). The fraction four (F4) with Rf value 0.35-0.40 was significant in reducing adverse effect of drought stress in host plants. Application of F4 resulted in delayed drooping point and higher drought tolerance index (3.34), induced stomatal closure (9.648 ), seed germination inhibition (12%), and reduced the GA3 induced -amylase activity in germinating barley seeds. On TLC, F4 turned colorless to orange color upon the spray of 2,4-dinitrophenylhydrazine reagent indicated the presence of aldehyde group. Supporting to this, the peaks between 9.8 to 10.0 ppm in 1H-NMR chromatogram confirmed the presence of aldehyde group. Upon LC-MS/MS analysis of crude extract of culture filtrate and F4 revealed the presence of compounds with the molecular mass 250.33 and 266.33. By analyzing these data, the identity of the bioactive compounds were predicted as xanthoxin and xanthoxic acid, which are well-known precursor of Abscisic acid (ABA) in plants. The present study concludes the capability of ABA analogue (xanthoxin like compounds) production by B. marisflavi CRDT-EB-1 and its involvement in inducing drought stress tolerance in the host plant.