title: Convergence of Light and ABA signaling on the ABI5 promoter.
abstract: Light is one of the most important environmental cues regulating multiple aspects of plant growth and development, and abscisic acid (ABA) is a plant hormone that plays important roles during many phases of the plant life cycle and in plants' responses to various environmental stresses. How plants integrate the external light signal with endogenous ABA pathway for better adaptation and survival remains poorly understood. Here, we show that BBX21 (also known as SALT TOLERANCE HOMOLOG 2), a B-box (BBX) protein previously shown to positively regulate seedling photomorphogenesis, is also involved in ABA signaling. Our genetic data show that BBX21 may act upstream of several ABA INSENSITIVE (ABI) genes and ELONGATED HYPOCOTYL 5 (HY5) in ABA control of seed germination. Previous studies showed that HY5 acts as a direct activator of ABI5 expression, and that BBX21 interacts with HY5. We further demonstrate that BBX21 negatively regulates ABI5 expression by interfering with HY5 binding to the ABI5 promoter. In addition, ABI5 was shown to directly activate its own expression, whereas BBX21 negatively regulates this activity by directly interacting with ABI5. Together, our study indicates that BBX21 coordinates with HY5 and ABI5 on the ABI5 promoter and that these transcriptional regulators work in concert to integrate light and ABA signaling in Arabidopsis thaliana.
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden ; Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.
authors.forename: Dongqing
authors.initials: D
authors.lastname: Xu
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China ; State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, China ; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, United States of America.
authors.forename: Jigang
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.
authors.forename: Sreeramaiah N
authors.initials: SN
authors.lastname: Gangappa
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.
authors.forename: Chamari
authors.initials: C
authors.lastname: Hettiarachchi
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Lin
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.
authors.forename: Mats X
authors.initials: MX
authors.lastname: Andersson
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China ; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, United States of America.
authors.forename: Xing Wang
authors.initials: XW
authors.lastname: Deng
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Holm
mesh_terms: D000040:Abscisic Acid / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D050976:Basic-Leucine Zipper Transcription Factors / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000235:genetics; D008027:Light; D009154:Mutation; D009687:Nuclear Proteins / Q000096:biosynthesis; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000254:growth & development; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: C409743:ABI5 protein, Arabidopsis; D029681:Arabidopsis Proteins; C556245:BBX21 protein, Arabidopsis; D050976:Basic-Leucine Zipper Transcription Factors; C109254:HY5 protein, Arabidopsis; D009687:Nuclear Proteins; D014157:Transcription Factors; D000040:Abscisic Acid