OsWAK11, a rice wall-associated kinase, regulates Cu detoxification by alteration the immobilization of Cu in cell walls

Wall-associated kinases (WAKs) are a family of receptor-like kinases (RLKs) with important roles against biotic and abiotic stresses in plants. Here, we reported that a rice WAK gene, OsWAK1 1, detoxifies excess copper by regulating the methylesterification of the cell wall. RNA interference- (RNAi-) mediated OsWAK11 knockdown in rice resulted in hypersensitivity to copper toxicity. This Cu hypersensitivity in OsWAK11-RNAi transgenic lines might result from more Cu uptake, which accumulated in the cytoplasm rather than the cell wall. Surprisingly, less Cu was accumulated in the cell wall pectin and hemicellulose of OsWAK11-RNAi transgenic lines than in wild-type plants, possibly because of decreased pectin methylesterase (PME) activity. We detected dramatically reduced expression of a key PME encoding gene, OsPME14, in OsWAK11-RNAi plants. Furthermore, disruption of OsPME14 expression could mimic the effects of OsWAK11 downregulation in plants challenged by excess Cu. Given that OsWAK11 expression is induced by excess Cu, our results indicate that plant cells activate OsWAK11 activity to modify the properties of the cell wall, thereby retaining Cu on the wall when subjected to excess Cu.