The MdVQ17/MdVQ37-MdWRKY100 module coordinates apple salt tolerance by modulating Na+/K+ homeostasis and ROS scavenging.

Abstract

Salt stress greatly affects the yield and quality of agricultural crops, limiting their geographic distribution. Valine-glutamine (VQ) motif-containing proteins function as transcriptional regulators of plant growth and stress responses. However, the role and underlying molecular mechanisms of VQ proteins in apple (Malus domestica) salt stress responses remain largely unknown. Here, MdVQ17 was identified as a salt-responsive gene that negatively regulates salt tolerance in apple plants by increasing the Na+/K+ ratio and suppressing reactive oxygen species (ROS) scavenging under salt stress. MdWRKY100, a WRKY transcription factor that enhances apple salt tolerance, was identified as an MdVQ17-interacting protein. MdWRKY100 directly bound to the Arabidopsis K⁺ TRANSPORTER 1-LIKe (MdAKT1-like) and PEROXIDASE 57 (MdPER57) promoters, activating their transcription. MdVQ17 inhibited the binding and transcriptional activation activity of MdWRKY100 at these promoters, thereby suppressing MdWRKY100-mediated regulation of Na+/K+ homeostasis and antioxidant enzyme activity. MdVQ37, another MdWRKY100-interacting VQ protein, modulated the MdWRKY100-mediated salt response through a similar mechanism. Overall, these findings reveal that the MdVQ17/MdVQ37-MdWRKY100 module co-regulates Na+/K+ homeostasis and ROS scavenging by modulating MdAKT1-like and MdPER57 expression, providing insights into how the VQ-WRKY complex influences salt tolerance in apple.