title: Stress physiology functions of the Arabidopsis histidine kinase cytokinin receptors.
abstract: Cytokinin signaling has complex effects on abiotic stress responses that remain to be fully elucidated. The Arabidopsis histidine kinases (AHKs), AHK2, AHK3 and CRE1 (cytokinin response1/AHK4) are the principle cytokinin receptors of Arabidopsis. Using a set of ahk mutants, we found dramatic differences in response to low water potential and salt stress among the AHKs. ahk3-3 mutants had increased root elongation after transfer to low water potential media. Conversely ahk2-2 was hypersensitive to salt stress in terms of root growth and fresh weight and accumulated higher than wild-type levels of proline specifically under salt stress. Strongly reduced proline accumulation in ahk double mutants after low water potential treatment indicated a more general role of cytokinin signaling in proline metabolism. Reduced P5CS1 (Δ(1) -pyrroline-5-carboxylate synthetase1) gene expression may have contributed to this reduced proline accumulation. Low water potential phenotypes of ahk mutants were not caused by altered abscisic acid (ABA) accumulation as all ahk mutants had wild-type ABA levels, despite the observation that ahk double mutants had reduced NCED3 (9-cis-epoxycartenoid dioxygenase3) expression when exposed to low water potential. No difference in osmoregulatory solute accumulation was detected in any of the ahk mutants indicating that they do not affect drought responsive osmotic adjustment. Overall, our examination of ahk mutants found specific phenotypes associated with AHK2 and AHK3 as well as a general function of cytokinin signaling in proline accumulation and low water potential induction of P5CS1 and NCED3 expression. These results show the stress physiology function of AHKs at a new level of detail.
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, 115, Taiwan.
authors.forename: M Nagaraj
authors.initials: MN
authors.lastname: Kumar
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, 115, Taiwan.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Verslues
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D050698:Glutamate-5-Semialdehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000071677:Histidine Kinase; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D064587:Osmoregulation / Q000187:drug effects / Q000235:genetics; D009997:Osmotic Pressure; D010641:Phenotype; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics*; D011956:Receptors, Cell Surface / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological / Q000235:genetics*; D014867:Water / Q000378:metabolism / Q000494:pharmacology
chemical_list: D029681:Arabidopsis Proteins; D009097:Multienzyme Complexes; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C583835:delta(1)-pyrroline-5-carboxylate synthetase, Arabidopsis; D014867:Water; D012965:Sodium Chloride; D000040:Abscisic Acid; D011392:Proline; D049308:Dioxygenases; C109043:9-cis-epoxy-carotenoid dioxygenase; D050698:Glutamate-5-Semialdehyde Dehydrogenase; D011494:Protein Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D000071677:Histidine Kinase; C000605492:AHK2 protein, Arabidopsis; C000605493:AHK3 protein, Arabidopsis; C421783:WOL protein, Arabidopsis