Plants have a series of response mechanisms to adapt when they are subjected to external stress. Calcium-dependent protein kinases (CDPKs) in plants function against a variety of abiotic stresses. We screened 17 CDPKs from drought- and salt-induced soybean transcriptome sequences. The phylogenetic tree divided CDPKs of rice, Arabidopsis and soybean into five groups (I–V). Cis-acting element analysis showed that the 17 CDPKs contained some elements associated with drought and salt stresses. Quantitative real-time PCR (qRT-PCR) analysis indicated that the 17 CDPKs were responsive after different degrees of induction under drought and salt stresses. GmCDPK3 was selected as a further research target due to its high relative expression. The subcellular localization experiment showed that GmCDPK3 was located on the membrane of Arabidopsis mesophyll protoplasts. Overexpression of GmCDPK3 improved drought and salt resistance in Arabidopsis. In the soybean hairy roots experiment, the leaves of GmCDPK3 hairy roots with RNA interference (GmCDPK3-RNAi) soybean lines were more wilted than those of GmCDPK3 overexpression (GmCDPK3-OE) soybean lines after drought and salt stresses. The trypan blue staining experiment further confirmed that cell membrane damage of GmCDPK3-RNAi soybean leaves was more severe than in GmCDPK3-OE soybean lines. In addition, proline (Pro) and chlorophyll contents were increased and malondialdehyde (MDA) content was decreased in GmCDPK3-OE soybean lines. On the contrary, GmCDPK3-RNAi soybean lines had decreased Pro and chlorophyll content and increased MDA. The results indicate that GmCDPK3 is essential in resisting drought and salt stresses.

Calmodulin-binding protein 60 (CBP60) members constitute a plant-specific protein family that plays an important role in plant growth and development. In the soybean genome, nineteen CBP60 members were identified and analyzed for their corresponding sequences and structures to explore their functions. Among GmCBP60A-1, which primarily locates in the cytomembrane, was significantly induced by drought and salt stresses. The overexpression of GmCBP60A-1 enhanced drought and salt tolerance in Arabidopsis, which showed better state in the germination of seeds and the root growth of seedlings. In the soybean hairy roots experiment, the overexpression of GmCBP60A-1 increased proline content, lowered water loss rate and malondialdehyde (MDA) content, all of which likely enhanced the drought and salt tolerance of soybean seedlings. Under stress conditions, drought and salt response-related genes showed significant differences in expression in hairy root soybean plants of GmCBP60A-1-overexpressing and hairy root soybean plants of RNAi. The present study identified GmCBP60A-1 as an important gene in response to salt and drought stresses based on the functional analysis of this gene and its potential underlying mechanisms in soybean stress-tolerance.