Study on the Heterologous Expression of GMCDPK SK5 Gene in Soybean ABA Signaling Pathway

In order to explore the ways of CDPKI family member GmCDPK SK5 participating in the defense against adversity stress, in this study, the promoter sequence of GmCDPK SK5 gene was cloned, and the GmCDPK SK5 pro∷GUS fusion plant expression vector was constructed to transform tobacco and Arabidopsis. The results showed that the application of exogenous ABA induced down-regulation of GmCDPK SK5 gene expression. Analysis of promoter cis-acting elements showed that the promoter contains 3 TATA boxes and 23 CAAT boxes basic transcription elements and a variety of cis-acting elements related to stress. GUS histochemical staining and quantitative expression analysis were used to study the response of GmCDPK SK5 promoter to exogenous Ca²⁺ and ABA. The results showed that the activity of GUS enzyme increased with the increase of Ca²⁺ concentration. Under the condition of 50 mmol·L^-1 Ca²⁺, the activity of GUS enzyme in the treatment group was 2.1 times of the control group. While the GUS activity decreased with the increase of ABA concentration. Under 0.01 μmol·L^-1 ABA, the GUS activity in the control group was 5 times of the treatment group. Therefore ABA can induce the down-regulation of GmCDPK SK5. In Arabidopsis, compared with WT and cpk4-1 mutant lines, GmCDPK SK5 overexpression lines were the most sensitive to exogenous ABA in seed germination, seedling growth and stomatal movement. The ABA-related genes（ABF2, ABF4, ABI5, RD29 A, RAB18 and KIN1） in the three lines were differentially expressed. The results showed that GmCDPK SK5 promoter responds to exogenous Ca²⁺ and ABA, and GmCDPK SK5 enhances the sensitivity of plants to ABA by affecting the expression of ABA-related genes.