As the most recently characterized group of plant hormones, brassinosteroids (BR) are involved in a number of physiological responses. Although many key components of the BR signaling pathway have been isolated and characterized, there is little information on detailed characterization of brassinosteroid-signaling kinase (BSK) proteins. In this study, Arabidopsis BSK5 was isolated and functionally analyzed. BSK5 transcripts were detected in various tissues, and were induced by abiotic stresses including salt and drought, as well as phytohormones of BR and abscisic acid (ABA). Arabidopsis loss-of-function mutant bsk5 exhibited sensitivity to salinity and ABA. Mutations of the BSK5 gene also altered the expression of several stress-regulated genes. We suggest that BSK5 responds to other signals as well as BR. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.