AHK5 histidine kinase regulates root elongation through an ETR1-dependent abscisic acid and ethylene signaling pathway in Arabidopsis thaliana. Iwama Ayako Tabata Satoshi The Arabidopsis thaliana genome encodes a small family of histidine (His) protein kinases, some of which have redundant functions as ethylene receptors, whereas others serve as cytokinin receptors. The most poorly characterized of these is authentic histidine kinase 5 (AHK5; also known as cytokinin-independent 2, CKI2). Here we characterize three independent ahk5 mutants, and show that they have a common phenotype. Our results suggest that AHK5 His-kinase acts as a negative regulator in the signaling pathway in which ethylene and ABA inhibit the root elongation through ETR1 (an ethylene receptor). 17202180 Kato Tomohiko 2007 Feb Mizuno Takeshi Yamashino Takafumi 375-80 Kakimoto Tatsuo Iwama Ayako et al. 2007 Feb. Plant Cell Physiol. 48(2):375-80. 48 Nagatani Akira Sato Shusei Sakakibara Hitoshi Tanaka Yasushi 2