GmWNK1, a Novel Serine/ Threonine Protein Kinase in Soybean Roots, Regulates ABA-Dependent Osmotic Stresses in Plants

摘要

In humans, WNKs ( with no Iysine kinases) regulate epithelial ion transport and their mutation causes a Mendelian syndrome of hypertension due to increased renal epithelial salt reabsorption. A related class of kinases was recently discovered in plants, but their functions are largely unknown. We have identified a novel root-specific WNK ortholog in soybean (Glycine max) , GmWNK1, using suppression subtractive hybridization. GmWNK1 transcripts are down-regulated by the phytohormone abscisic acid ( ABA ) , which plays a critical role in the adaptation of plants to osmotic stresses. The expression of GmWNK1 was also inhibited by salt and mannitol, inducers of ABA signaling, but unaffected by non-osmotic stresses such as nutrient deficiency or metal toxicity. Using a bacterial two-hybrid system, GmWNK1 was found to interact with a key enzyme of ABA metabolism, the ABA 8'-hydroxylase, GmCYP707A1, via its carboxy-terminal regulatory domain. Transgenic overexpression of GmWNK1 in Arabidopsis thaliana plants conferred a classic ABA-insensitive phenotype, with a reduced degree of seed dormancy and enhanced tolerance to ABA, salt, and mannitol. Endogenous levels of ABA, and the expression of specific ABA-responsive genes, were significantly higher in GmWNK1 transgenic plants than in their wild type counterparts under osmotically-challenged conditions. Together, these data provide evidence that GmWNK1 negatively regulates stress-responsive ABA signaling and metabolism in plants via an interaction with the ABA 8'-hydroxylase GmCYP707A, and these WNKs are evolutionarily-conserved regulators of the cellular response to osmotic stress.