title: The Heat Stress Factor HSFA6b Connects ABA Signaling and ABA-Mediated Heat Responses.
abstract: Heat stress response (HSR) is a conserved mechanism developed to increase the expression of heat shock proteins (HSPs) via a heat shock factor (HSF)-dependent mechanism. Signaling by the stress phytohormone abscisic acid (ABA) is involved in acquired thermotolerance as well. Analysis of Arabidopsis (Arabidopsis thaliana) microarray databases revealed that the expression of HSFA6b, a class A HSF, extensively increased with salinity, osmotic, and cold stresses, but not heat. Here, we show that HSFA6b plays a pivotal role in the response to ABA and in thermotolerance. Salt-inducible HSFA6b expression was down-regulated in ABA-insensitive and -deficient mutants; however, exogenous ABA application restored expression in ABA-deficient, but not -insensitive plants. Thus, ABA signaling is required for proper HSFA6b expression. A transcriptional activation assay of protoplasts revealed that ABA treatment and coexpression of an ABA signaling master effector, ABA-RESPONSIVE ELEMENT-BINDING PROTEIN1, could activate the HSFA6b promoter. In addition, HSFA6b directly bound to the promoter of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN2A and enhanced its expression. Analysis of ABA responses in seed germination, cotyledon greening, and root growth as well as salt and drought tolerance in HSFA6b-null, overexpression, and dominant negative mutants revealed that HSFA6b is a positive regulator participating in ABA-mediated salt and drought resistance. Thermoprotection tests showed that HSFA6b was required for thermotolerance acquisition. Our study reveals a network in which HSFA6b operates as a downstream regulator of the ABA-mediated stress response and is required for heat stress resistance. This new ABA-signaling pathway is integrated into the complex HSR network in planta.
authors: Institute of Plant Biology and Department of Life Science, National Taiwan University, Taipei 10617, Taiwan.
authors: Ya-Chen
authors: 0000-0002-2090-0378
authors: YC
authors: Huang
authors: Institute of Plant Biology and Department of Life Science, National Taiwan University, Taipei 10617, Taiwan.
authors: Chung-Yen
authors: 0000-0001-8847-6537
authors: CY
authors: Niu
authors: Institute of Plant Biology and Department of Life Science, National Taiwan University, Taipei 10617, Taiwan.
authors: Chen-Ru
authors: CR
authors: Yang
authors: Institute of Plant Biology and Department of Life Science, National Taiwan University, Taipei 10617, Taiwan jinnt@ntu.edu.tw.
authors: Tsung-Luo
authors: 0000-0002-5185-7691
authors: TL
authors: Jinn
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D063990:Gene Ontology; D053263:Gene Regulatory Networks; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D018869:Heat-Shock Response / Q000235:genetics*; D006358:Hot Temperature; D015151:Immunoblotting; D018613:Microscopy, Confocal; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology; D000071436:Thermotolerance / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C000623167:HSFA6b protein, Arabidopsis; D006360:Heat-Shock Proteins; D010937:Plant Growth Regulators; D014157:Transcription Factors; D012965:Sodium Chloride; D000040:Abscisic Acid