Inverse modulation of the energy sensor Snf1-related protein kinase 1 on hypoxia adaptation and salt stress tolerance in Arabidopsis thaliana

Terrestrial plants are exposed to complex stresses of high salt-induced abscisic acid (ABA) and submergence-induced hypoxia when seawater floods fields. Many studies have investigated plant responses to individual stress conditions, but not so much for coupled or sequentially imposed stresses. We examined molecular regulatory mechanisms of gene expression underlying the cellular responses involved in crosstalk between salt and hypoxia stresses. Salt/ABA- and AtMYC2-dependent induction of a synthetic ABA-responsive element and the native RD22 promoters were utilized in our cell-based functional assays. Such promoter-based reporter induction was largely inhibited by hypoxia and hypoxia-inducible AKIN10 activity. Biochemical analyses showed that AKIN10 negatively modulates AtMYC2 protein accumulation via proteasome activity upon AKIN10 kinase activity-dependent protein modification. Further genetic analysis using transgenic plants expressing AKIN10 provided evidence that AKIN10 activity undermined AtMYC2-dependent salt tolerance. Our findings unravel a novel molecular interaction between the key signalling constituents leading crosstalk between salt and hypoxia stresses in Arabidopsis thaliana under the detrimental condition of submergence in saltwater.