A newly isolated Bacillus pumilus strain SH-9 modulates response to drought stress in soybean via endogenous phytohormones and gene expression (Daegu, South Korea)

초록

Drought stress hampers plant growth and productivity. Some microorganisms mitigate stress in plants; however, the molecular mechanism by which they interact with plants in mitigating stress remains unknown. This study aimed to determine the mechanism by which plant growth-promoting rhizobacteria modulate drought stress in soybean. Results indicated that B. pumilus SH-9 (SH-9) produced indole acetic acid and siderophore, and had capacity for phosphate solubilization. The test for polyethylene glycol 6000 (PEG) tolerance, showed that SH-9 could withstand high PEG concentration (up to 30 %). The isolate was identified a B. pumilus strain using a 16 s ribosomal DNA gene sequence. Inoculation of soybeans with SH-9 enhanced soybean plant growth and biomass by 20 %, even under high drought stress. This was due to a reduction of the endogenous phytohormone (abscisic acid) and upregulation of the antioxidant defense system (SOD, POD, APX, and GSH) by SH-9. Furthermore, the transcription factors GmDREB2, GmbZIP1, and GmNCED3 were involved. Inoculation with SH-9 also improved physio-morphological characteristics such as biomass, chlorophyll, seedling length, and relative water contents in the stressed plant. Overall, the findings of this study indicated that SH-9 enhances plant growth by promoting phosphate solubilization, siderophore, and exopolysaccharides. We, therefore, conclude that SH-9 is a drought-tolerant variant that can improve plant growth even under drought stress via modulation of expression of the phytohormone gene, and antioxidant profile.

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