SOS3 from Avicennia marina Enhances Salt Stress Tolerance of Arabidopsis thaliana

Abiotic stress poses a serious challenge in agriculture. Salinity inhibits crop growth and yields by disrupting ionic homeostasis and osmotic balance. One critical mechanism of salt tolerance is the activation of the Salt Overly Sensitive (SOS) signaling pathway. Investigating this pathway in halophytic plants offers valuable insights into the molecular mechanisms underlying salt stress tolerance. This study explores the structure and function of SOS3/CBL4 from the gray mangrove, Avicennia marina (AmSOS3). Sequence analysis revealed that AmSOS3 shares significant similarities with orthologs of SOS3/CBL4, including Arabidopsis thaliana (AtSOS3). All essential functional domains of SOS3, including the four EF-hands, as well as the N-myristoylation and S-acylation motif, were conserved in AmSOS3. Structural modeling, using Modeller, predicted that AmSOS3 forms a homodimer stabilized by a hydrogen bond at the serine 140 position. Functional characterization further demonstrated that AmSOS3 complements the sos3-1 mutation in A. thaliana, thus confirming that AmSOS3 is an ortholog of AtSOS3. Overexpression of AmSOS3 in wild-type A. thaliana enhanced tolerance under salinity stress. The transgenic lines displayed reduced reactive oxygen species (ROS) accumulation and increased ROS-scavenging enzyme activity. These findings indicate that AmSOS3 plays a critical role in improving salt stress tolerance and maintaining cellular homeostasis.