Integrated phytohormone production by the plant growth-promoting rhizobacterium <i>Bacillus tequilensis</i> SSB07 induced thermotolerance in soybean

As a result of climate change, crops often experience high-temperature stress that can drastically hinder plant growth and development. In soybean, an economically important crop that is highly sensitive to heat stress, the use of plant growth-promoting rhizobacteria (PGPRs) represents a promising strategy for countering the negative effects of heat stress. Accordingly, a novel strain of Bacillus tequilensis (i.e. SSB07) that grows actively at high temperatures was isolated, identified, and characterized in the present study. SSB07 improved the growth of Chinese cabbage seedlings and was shown to produce the gibberellins GA1, GA3, GA5, GA8, GA19, GA24, and GA53, as well as indole-3-acetic acid and abscisic acid. The application of B. tequilensis SSB07 was also found to increase the shoot length and biomass, leaf development, and photosynthetic pigment contents of soybean plants, and under heat stress, SSB07 inoculation significantly increased the endogenous jasmonic acid and salicylic acid contents of the phyllosphere and significantly down-regulated the production of stress-responsive ABA. Thus, B. tequilensis SSB07 shows promise for countering the negative effects of climate change on crop growth and development.