title: A small plant-specific protein family of ABI five binding proteins (AFPs) regulates stress response in germinating Arabidopsis seeds and seedlings.
abstract: The transcription factor ABA-Insensitive5 (ABI5) is a key regulator of ABA signaling and stress response in Arabidopsis seeds and seedlings. Potential ABI5-interacting proteins were identified by a yeast two-hybrid screen; the most prevalent interactors were a family of four highly conserved plant-specific proteins with no domains of known function, but homology to a previously characterized ABI Five Binding Protein (AFP). This study compares expression and function of the family members. The AFPs are induced by ABA and/or dehydrating stresses in young seedlings, but the developmental timing of their induction differs. Mutations in AFP1 or AFP2 result in increased sensitivity to ABA and salt, whereas afp4 mutants are mildly ABA-resistant. AFP2, like AFP1, acts epistatically to ABI5. Reduced germination or seedling growth of the mutants under stress correlates with a higher level of ABI5 protein when compared to wild-type seedlings, but it is not clear whether this is a cause or effect of the reduced growth. Although both ABI5 and the AFPs are ABA-induced, the ABI5:AFP ratio increases at high ABA concentrations, maintaining growth inhibition under severe stress. An AFP2:GFP fusion, which complements the afp2 mutation, is nuclear-localized in seedlings exposed to stress, but becomes delocalized before being degraded following removal of stress. The AFPs may also interact to varying extents with many ABI5-related bZIP transcription factors. This study suggests that germination and seedling growth are regulated by antagonistic interactions among at least two functionally redundant families, the AFPs and the ABI5-related proteins, providing a mechanism to fine-tune seedling stress responses.
authors.affiliation: Molecular, Cellular, and Developmental Biology Department, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Mary Emily
authors.initials: ME
authors.lastname: Garcia
authors.forename: Tim
authors.initials: T
authors.lastname: Lynch
authors.forename: Julian
authors.initials: J
authors.lastname: Peeters
authors.forename: Chris
authors.initials: C
authors.lastname: Snowden
authors.forename: Ruth
authors.initials: R
authors.lastname: Finkelstein
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000235:genetics; D017360:Arabidopsis / Q000196:embryology / Q000235:genetics* / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D009154:Mutation; D036226:Seedlings / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: C409743:ABI5 protein, Arabidopsis; C000616520:AFP1 protein, Arabidopsis; C000616521:AFP2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D000040:Abscisic Acid