Bacillus butanolivorans KJ40 contributes alleviation of drought stress in pepper plants by modulating antioxidant and polyphenolic compounds

Abstract

Drought causes severe economic losses by disturbing normal plant growth and productivity in agricultural systems. Plant-associated beneficial microorganisms have been studied to alleviate drought stress by inducing tolerance to stress. In this study, we investigated plant responses to drought stress by withholding irrigation water, as well as changes in polyphenol content, including flavonoids, in the fruits of Bacillus butanolivorans KJ40-treated pepper plants. When KJ40-treated plants were exposed to water stress by withholding water, lipid peroxidation significantly decreased, peroxidase and glutathione peroxidase were highly activated; meanwhile, catalase and superoxide dismutase decreased compared to control plants. Moreover, KJ40-treated plants strongly triggered drought tolerance-related genes, including Capsicum annuum dehydrin (Cadhn), small heat shock protein (sHSP), △1-pyrroline-5-carboxylate synthetase (P5CS), △1-pyrroline-5-carboxylate reductase (P5CR), bZIP transcription factor 1 (bZIP1), lipoxygenase 1(LOX1), and coronatine insensitive 1 (COI1) under drought stress conditions. In a greenhouse test, soil moisture and stomatal conductance were highly maintained in KJ40-treated plants during drought. Two weeks after re-watering, fruit weight and number were higher than that of the untreated control. Differential accumulation and alteration of polyphenol contents, including flavonoids, were observed in fruits of KJ40-treated plants, and capsaicin, dihydrocapsaicin, and naringenin were decreased. However, luteolin and catechin were increased compared to those of control plants. These findings indicate that B. butanolivorans KJ40 can alleviate drought stress and induce tolerance by activation of peroxidase and glutathione peroxidase and upregulation of gene expression of Cadhn, sHSP, proline (P5CS and P5CR)-, ABA (bZIP1 and NCED1)-, and JA (LOX1 and COI1)-related genes, as well as changing polyphenol content in KJ40-treated pepper plants under drought stress.