The photoperiod regulator E1 family negatively modulates salt tolerance by directly repressing GmCIPK25 expression in soybean.

Soybean (Glycine max [L.] Merr.) is an important crop whose productivity is severely constrained by salinity. Here, we identify the photoperiod regulator E1 family as negative regulators of soybean salt tolerance. Under salt stress, the e1 e1la e1lb triple mutant (e1-3m) show higher antioxidant enzyme activities and proline accumulation, together with reduced hydrogen peroxide and malondialdehyde levels, whereas E1 overexpression increases salt sensitivity. Integrated RNA-seq and ChIP-seq analyses identify GmCIPK25, a positive regulator of salt tolerance, as a direct target of E1. E1, E1La, and E1Lb bind directly to the GmCIPK25 promoter and repress its transcription. Knockdown of GmCIPK25 attenuates the enhanced salt tolerance of e1-3m, while loss of GmCIPK25 function in the wild-type background increased salt sensitivity. Thus, the E1 family negatively regulates salt tolerance by repressing GmCIPK25, which compromises reactive oxygen species (ROS)-scavenging capacity and osmotic adjustment. These findings link photoperiodic regulation to salt-stress responses and identify GmCIPK25 as a potential target for improving soybean salt tolerance.