title: Cytokinin antagonizes ABA suppression to seed germination of Arabidopsis by downregulating ABI5 expression.
abstract: Abscisic acid (ABA) and cytokinin are key hormones controlling plant development. How ABA and cytokinin interplay to control the transition from a dry seed into a young seedling remains elusive. Here we undertook a gain-of-function genetic screen to identify ABA-insensitive mutants during seed germination in Arabidopsis using an estradiol-inducible approach. In the presence of estradiol, one of these mutants gim1 (germination insensitive to ABA mutant 1) exhibited an elevated level of cytokinin that was attributed to the estradiol-induced expression of AtIPT8 that encodes an isopentenyltransferase for the biosynthesis of cytokinins. Our data on OE-2 and Com-1 transgenic plants carrying the ectopically expressing AtIPT8 gene indicated that the elevation of cytokinin level was responsible for the ABA-insensitivity of gim1 seed germination. Further analyses on alterations of gene transcriptomes in the gim1 mutant demonstrated that the expression of some ABA-inducible genes, including ABI5, was reduced, and could not be restored by exogenous ABA treatment. Moreover, we also failed to observe the ABA-mediated repression of a family of cytokinin signal transducers and transcription repressors called type-A ARR4, ARR5 and ARR6 in the gim1 seedlings. Further analysis demonstrated that type-A ARR4, ARR5 and ARR6 could negatively regulate ABI5 expression, and the physical interaction of ABI5 and type-A ARR4, ARR5 and ARR6 proteins was detected. In summary, our study suggests that the interaction of ABA and cytokinin during seed germination and seedling growth can be mediated by the interplay of transcriptional regulators in Arabidopsis.
authors.affiliation: Department of Cell and Developmental Biology, College of Life Science, Wuhan University, Wuhan 430072, China.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Wang
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Tiantian
authors.initials: T
authors.lastname: Ye
authors.forename: Shujuan
authors.initials: S
authors.lastname: Zhao
authors.forename: Zhao
authors.initials: Z
authors.lastname: Liu
authors.forename: Yu-Qi
authors.initials: YQ
authors.lastname: Feng
authors.forename: Yan
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D003583:Cytokinins / Q000032:analysis / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D018525:Germination / Q000502:physiology; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified; D025941:Protein Interaction Mapping; D036226:Seedlings / Q000235:genetics / Q000502:physiology; D012639:Seeds / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D059467:Transcriptome
chemical_list: C409743:ABI5 protein, Arabidopsis; C113359:ARR4 protein, Arabidopsis; C549195:ARR5 protein, Arabidopsis; C586059:ARR6 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D003583:Cytokinins; D010937:Plant Growth Regulators; D014157:Transcription Factors; D000040:Abscisic Acid; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase