Drought stress impairs crop growth and productivity. Stress-associated proteins (SAPs), a class of zinc finger proteins containing the A20/AN1 domain, function in various stress responses in plants. However, little is known about the function of SAPs in drought-stress responses in soybean, an oil and protein crop. We report that a GmSAP5 protein confers drought tolerance by increasing sensitivity to abscisic acid (ABA) and reducing stomatal aperture. Overexpression and RNA interference of GmSAP5 in soybean hairy roots resulted in elevated resistance and sensitivity to drought stress, respectively. ABA and proline contents increased in GmSAP5-overexpressing plants under water-deficit conditions. Lower water loss rates and higher relative water contents were observed in GmSAP5-overexpressing plants, resulting in increased drought-stress resistance. A yeast one-hybrid assay and luciferase transient transcriptional activity assay showed that GmAREB3, an AREB/ABF transcription factor, could bind to the promoter of GmSAP5 and activate its expression. These results suggest that GmSAP5 acts downstream of GmAREB3 and improves drought-stress resistance by mediating ABA signaling.

Plant AT-rich sequence and zinc binding (PLATZ) transcription factors are a class of plant specific zinc-dependent DNA-binding proteins that function in abiotic stress response and plant development. In this study, 31 GmPLATZ genes were identified in soybean. GmPLATZ17 was down-regulated by drought and exogenous abscisic acid. Transgenic Arabidopsis and soybean hairy roots overexpressing GmPLATZ17 showed drought sensitivity and inhibition of stress-associated gene transcription. In contrast, suppressed expression of GmPLATZ17 led to increased drought tolerance in transgenic soybean hairy roots. The GmPLATZ17 protein was verified to interact physically with the GmDREB5 transcription factor, and overexpression of GmDREB5 increased drought tolerance in soybean hairy roots. Interaction of GmPLATZ17 with GmDREB5 was shown to interfere with the DRE-binding activity of GmDREB5, suppressing downstream stress-associated gene expression. These results show that GmPLATZ17 inhibits drought tolerance by interacting with GmDREB5. This study sheds light on PLATZ transcription factors and the function of GmPLATZ17 in regulating drought sensitivity.