title: Analysis of cytokinin mutants and regulation of cytokinin metabolic genes reveals important regulatory roles of cytokinins in drought, salt and abscisic acid responses, and abscisic acid biosynthesis.
abstract: Cytokinins (CKs) regulate plant growth and development via a complex network of CK signaling. Here, we perform functional analyses with CK-deficient plants to provide direct evidence that CKs negatively regulate salt and drought stress signaling. All CK-deficient plants with reduced levels of various CKs exhibited a strong stress-tolerant phenotype that was associated with increased cell membrane integrity and abscisic acid (ABA) hypersensitivity rather than stomatal density and ABA-mediated stomatal closure. Expression of the Arabidopsis thaliana ISOPENTENYL-TRANSFERASE genes involved in the biosynthesis of bioactive CKs and the majority of the Arabidopsis CYTOKININ OXIDASES/DEHYDROGENASES genes was repressed by stress and ABA treatments, leading to a decrease in biologically active CK contents. These results demonstrate a novel mechanism for survival under abiotic stress conditions via the homeostatic regulation of steady state CK levels. Additionally, under normal conditions, although CK deficiency increased the sensitivity of plants to exogenous ABA, it caused a downregulation of key ABA biosynthetic genes, leading to a significant reduction in endogenous ABA levels in CK-deficient plants relative to the wild type. Taken together, this study provides direct evidence that mutual regulation mechanisms exist between the CK and ABA metabolism and signals underlying different processes regulating plant adaptation to stressors as well as plant growth and development.
authors: RIKEN Plant Science Center, Yokohama, Kanagawa 230-0045, Japan.
authors: Rie
authors: R
authors: Nishiyama
authors: Yasuko
authors: Y
authors: Watanabe
authors: Yasunari
authors: Y
authors: Fujita
authors: Dung Tien
authors: DT
authors: Le
authors: Mikiko
authors: M
authors: Kojima
authors: Tomás
authors: T
authors: Werner
authors: Radomira
authors: R
authors: Vankova
authors: Kazuko
authors: K
authors: Yamaguchi-Shinozaki
authors: Kazuo
authors: K
authors: Shinozaki
authors: Tatsuo
authors: T
authors: Kakimoto
authors: Hitoshi
authors: H
authors: Sakakibara
authors: Thomas
authors: T
authors: Schmülling
authors: Lam-Son Phan
authors: LS
authors: Tran
mesh_terms: D000040:Abscisic Acid / Q000096:biosynthesis* / Q000494:pharmacology; D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003583:Cytokinins / Q000235:genetics* / Q000378:metabolism*; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010641:Phenotype; D054046:Plant Stomata / Q000378:metabolism; D012492:Salts / Q000378:metabolism*; D012639:Seeds / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013312:Stress, Physiological
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D012492:Salts; D000040:Abscisic Acid