Accumulation of γ-sitosterol in response to drought stress and its interaction with plant stress signaling receptors in Brassica juncea

Drought has the most detrimental effects on plant growth, function, and productivity. In order to adapt, plants either express genes/proteins or produce secondary metabolites like terpenoids, steroids, and sterols. Phytosterols are naturally occurring compounds that play a vital role in plant growth and stress tolerance. Plant tolerance is provided by the phytosterol composition, which also affects the development of other agronomic features under drought stress. Therefore, in the present investigation, metabolic profiling was performed to determine the phytosterol composition under different concentrations of mannitol stress in Brassica juncea seedlings. The growth of the seedlings significantly decreased with the increase in the concentration of mannitol. Similar observation was also noted for physiological and biochemical parameters. Using the methanolic extract of unstressed and stressed B. juncea seedlings, metabolic profiling was performed using Gas Chromatography-Mass Spectrometry. Metabolomic profiling showed 119 phytocompounds out of which four phytocompounds γ-sitosterol, phytol, Ethyl alpha-d-glucopyranoside and hexadecanoic acid were abundant. Molecular docking was performed to determine the interaction of selected phytosterols with known plant stress signalling receptors and their possible role in signalling during drought stress. In silico molecular interaction showed strong binding affinity of γ-sitosterol with all the selected plant stress receptors. The expression of DWF1 and CYP710A1 gene showed co-relation with the γ-sitosterol content under drought stress. The γ-sitosterol content was also analyzed using HPLC. Not much is known about the mechanism of γ-sitosterol signalling in plants. Therefore, further investigation is required for understanding its role in the signalling pathway.