| Summary: | Soybean (<i>Glycine max</i> (Linn.) Merr.) is a widely-cultivated crop, the yield of which is markedly affected by adverse environmental conditions. Soil salinization, in particular, has led to the degradation of agricultural land, resulting in poor plant growth and decreased crop yields. In plants, serine/threonine protein kinases (STKs) are involved in the plant response to a variety of abiotic stresses. Our previous study identified a transcription factor (GmWRKY20) involved in plant stress resistance, which can directly regulate the expression of GmSTK12. Here, we investigated the effect of the stress-responsive gene <i>GmSTK12</i> (Glyma.12g198200), which encodes a serine/threonine protein kinase, on soybean salt tolerance. Overall, the overexpression of <i>GmSTK12</i> (<i>GmSTK12</i>-OE) resulted in increased salt tolerance. Under salt stress, <i>GmSTK12</i>-OE soybeans exhibited significantly increased chlorophyll and proline (PRO) contents; decreased relative electrical conductivity; decreased malondialdehyde (MDA) and superoxide anion (O2<sup>−</sup>) contents; and increased activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). The nitroblue tetrazolium chloride (NBT) staining experiment further confirmed the reduced accumulation of reactive oxygen species (ROS) in <i>GmSTK12</i>-OE soybean leaves. We further determined the Na<sup>+</sup> and K<sup>+</sup> contents in soybean leaves and roots and found that the Na<sup>+</sup> content and Na<sup>+</sup>/K<sup>+</sup> ratio in <i>GmSTK12</i>-OE soybean leaves and roots were significantly lower than those of WT (williams82) soybeans. Furthermore, quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of three SOS pathway genes (<i>GmSOS1</i>, <i>GmSOS2a,</i> and <i>GmSOS2b</i>) was upregulated in <i>GmSTK12</i>-OE soybeans under salt stress. Taken together, the results indicate that GmSTK12 is involved in the mechanism of soybean response to salt stress.
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