Functional analysis of McSnRK1 (SNF1-related protein kinase 1) in regulating Na/K homeostasis in transgenic cultured cells and roots of halophyte Mesembryanthemum crystallinum.

KEY MESSAGE: Transgenic callus and roots of ice plant with altered SnRK1 function were established using Agrobacterium-mediated transformation. The role of McSnRK1 in controlling Na+ influx and Na/K ratio was demonstrated. SnRK1 kinases (SNF1-related protein kinase1) control metabolic adaptation during energy deprivation and regulate protective mechanisms against environmental stress. Yeast SNF1 activates a P-type ATPase, the Na+ exclusion pump, under glucose starvation. The involvement of plant SnRK1 in salt stress response is largely unknown. We previously identified a salt-induced McSnRK1 in the halophyte ice plant (Mesembryanthemum crystallinum). In the current study, the function of McSnRK1 in salt tolerance was analyzed in transgenic cultured cells and roots of ice plant. Ice plant callus constitutively expressed a high level of McSnRK1 and introducing the full-length McSnRK1 did not alter the Na/K ratio at 24 h after 200 mM NaCl treatment. However, interfering with McSnRK1 activity by introducing a truncate McSnRK1 to produce a dominant-negative form of McSnRK1 increased cellular Na+ accumulation and Na/K ratio. As a result, the growth of cultured cells diminished under salt treatment. Hydroponically grown ice plants with roots expressing full-length McSnRK1 had better growth and lowered Na/K ratio compared to the wild-type or vector-only plants. Roots expressing a truncate McSnRK1 had reduced growth and high Na/K ratio under 400 mM NaCl treatment. The changes in Na/K ratio in transgenic cells and whole plants demonstrated the function of SnRK1 in controlling Na+ flux and maintaining Na/K homeostasis under salinity. The Agrobacterium-mediated transformation system could be a versatile tool for functional analysis of genes involved in salt tolerance in the ice plant.