The growth promotion of Arabidopsis thaliana by Serratia sp. H6 requires the metabolic stress sensor SNF1-related protein kinase 1 (SnRK1)

The SNF1 (sucrose non-fermenting1)-related protein kinase1 (SnRK1) is the plant ortholog of the budding yeast SNF1 and mammalian AMP-activated protein kinase (AMPK). These conserved proteins function as metabolic sensors activated in response to decreasing energy levels. Here, we analyzed the role of SnRK1 in the interaction of Arabidopsis thaliana with the plant growth-promoting rhizobacterium (PGPR) Serratia sp. H6, under low-energy conditions, using molecular and pharmacological approaches. In the absence of sucrose in the plant growth medium, Serratia sp. H6 phytostimulated and promoted the growth of the A. thaliana mutant kin10, which has impaired SnRK1 catalytic activity, as assessed by changes in lateral root number, root length, and fresh weight. Under the same growth conditions, the mammalian AMPK inhibitor dorsomorphin (DM) at 5 μM notably decreased plant growth and cell division in the root meristem, inhibiting the phytostimulation by the rhizobacterium. In contrast, the addition of resveratrol (RSV) at 25 or 50 μM, an activator of mammalian AMPK, in the presence of Serratia sp. H6 and without sucrose, improved cell division in the root meristem, the formation of lateral roots, and the phytostimulatory effects on A. thaliana. RSV was unable to restore phytostimulation in kin10 and snrk1.3 mutant plants. These pharmacological studies suggest that SnRK1 activity is required for the growth promotion of A. thaliana by the rhizobacterium under low-energy levels. Our findings show that SnRK1 plays a key role in the growth of A. thaliana promoted by Serratia sp. H6, under metabolic stress.