Antisense expression of a cell wall-associated protein kinase, WAK4, inhibits cell elongation and alters morphology

The Arabidopsis cell wall-associated receptor-like kinase (WAK) gene family contains five highly related members whose products are suited for exchang ing signals between the intracellular and extracellular compartments. WAK m embers are expressed in specific organs and regulated differentially by var ious biotic and abiotic factors. To gain further insight into how WAKs func tion during development, we used a glucocorticoid-inducible system to expre ss ectopically the WAK4 antisense gene. The induced expression of the WAK4 antisense gene resulted in a significant decrease of WAK proteins. Ninety-s ix hours after the induction of WAK4 antisense expression, WAK proteins bec ame undetectable, Cell elongation was impaired, and lateral root developmen t was blocked. The level of WAK protein could be controlled by the concentr ation of the applied inducer, dexamethasone, and was correlated with the se verity of the cell elongation inhibition phenotype. These results suggest t hat the WAKs serve a vital role in cell elongation and are required for pla nt development.