Stress-Activated Protein Kinase OsSAPK7 Regulates Salt- Stress Tolerance by Modulating Diverse Stress-Defensive Responses in Rice

Soil salinity is an environmental threat limiting rice productivity. Identification of salinity tolerance genes and exploitation of their mechanisms in plants are vital for crop breeding. In this study, the function of stress-activated protein kinase 7 (OsSAPK7), a SnRK2 family member, was characterized in response to salt stress in rice. Compared with variety 9804, OsSAPK7-overexpression plants had a greater survival rate, increased chlorophyll and proline contents, and superoxide dismutase and catalase activities at the seedling stage under salt-stress conditions, as well as decreased sodium potassium ratio (Na+/K+) and malondialdehyde contents. After salt stress, the OsSAPK7 knockout plants had lower survival rates, increased Na+/K+ ratios and malomdiadehyde contents, and decreased physiological parameters compared with 9804. These changes in transgenic lines suggested that OsSAPK7 increased the salt tolerance of rice by modulating ion homeostasis, redox reactions and photosynthesis. The results of RNA-Seq indicated that genes involved in redox-dependent signaling pathway, photosynthesis and zeatin synthesis pathways were significantly down-regulated in the OsSAPK7 knockout line compared with 9804 under salt-stress condition, which confirmed that OsSAPK7 positively regulated salt tolerance by modulating diverse stress-defensive responses in rice. These findings provided novel insights for the genetic improvement of rice and for understanding the regulatory mechanisms of salt-stress tolerance.