title: ABI4 represses the expression of type-A ARRs to inhibit seed germination in Arabidopsis.
abstract: The plant hormone abscisic acid (ABA) plays a crucial role in regulating seed germination and post-germination growth. ABSCISIC ACID INSENSITIVE4 (ABI4), an APETALA2 (AP2)-type transcription factor, is required for the ABA-mediated inhibition of seed germination. Cytokinins promote seed germination and seedling growth by antagonizing ABA signaling. However, the interaction between ABA and cytokinin signaling during seed germination remains unclear. Here, we report that ABA signaling downregulates Arabidopsis response regulators (ARRs), a class of cytokinin-inducible genes, during seed germination and cotyledon greening. We found that the application of exogenous ABA repressed the expression of type-A ARRs in Arabidopsis seeds and seedlings. Among the type-A ARR family members, the expression of ARR6, ARR7 and ARR15 was upregulated in ABA-deficient mutants, indicating that the transcriptional inhibition of type-A ARRs requires the ABA signaling pathway. Single and multiple mutations of these ARRs resulted in increased ABA sensitivity during germination and cotyledon greening; overexpression of ARR7 or ARR15 led to an ABA-insensitive phenotype. These observations suggest that type-A ARRs inhibit the ABA response during seed germination and cotyledon greening. Further analysis showed that ABI4 negatively regulated the transcription of ARR6, ARR7 and ARR15 by directly binding to their promoters. Genetic analysis showed that loss-of-function mutations of ARR7 and ARR15 partially rescued the ABA insensitivity of abi4-1. Thus, this study revealed that ABI4 plays a key role in ABA and cytokinin signaling by inhibiting the transcription of type-A ARRs to inhibit seed germination and cotyledon greening.
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: Xiaozhen
authors.initials: X
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: Zhizhong
authors.initials: Z
authors.lastname: Gong
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: Shuhua
authors.initials: S
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: Yiting
authors.initials: Y
authors.lastname: Shi
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000235:genetics*; D009154:Mutation; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C470421:ABI4 protein, Arabidopsis; C470377:ARR15 protein, Arabidopsis; C586059:ARR6 protein, Arabidopsis; C507238:ARR7 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D000040:Abscisic Acid
keywords: ABI4; Arabidopsis; abscisic acid; cytokinin; seed germination; transcriptional regulation; type-A ARRs