Abstract: Alkaline stress is a major constraint on crop growth and development and negatively impacts soybean (Glycine max) production and yield. Despite the remarkable progress that has been made in investigating beneficial microbes that facilitate plant growth and development, the role of rhizobacteria in regulating alkaline tolerance in soybean remains poorly understood. Here, we isolated Klebsiella sp. strain B7 from the Suaeda glauca roots and found that it enhances the alkaline tolerance of soybean by secreting pyruvic acid. Metabolome and RT-qPCR analysis of soybean roots indicated that high levels of pyruvic acid secreted by B7 activated the expression of genes involved in pyruvic acid metabolism and increased L-malic acid accumulation in soybean roots, thereby effectively mitigating reactive oxygen species induced by alkaline stress. Overexpression of these pyruvic acid metabolism-associated genes greatly enhanced alkaline tolerance of soybean and ATP-citrate lyase activity, further confirming the positive role of pyruvic acid in L-malic acid biosynthesis and alkaline tolerance in soybean. Notably, the B7 application to alkaline soil enhanced the soybean yield. Moreover, B7 recruited more beneficial microbes and shaped the composition of the rhizosphere bacterial community of soybean plants. These findings highlight the vital function of rhizobacteria strain B7 in enhancing alkaline tolerance in soybean, thus providing further evidence for the crucial role of plant growth-promoting rhizobacteria in the abiotic stress response of soybean.

Key words: alkaline stress, plant growth, pyruvic acid, rhizobac-teria, soybean