title: AtHsp70-15-deficient Arabidopsis plants are characterized by reduced growth, a constitutive cytosolic protein response and enhanced resistance to TuMV.
abstract: Arabidopsis thaliana contains 18 genes encoding Hsp70s. This heat shock protein superfamily is divided into two sub-families: DnaK and Hsp110/SSE. In order to functionally characterize members of the Hsp70 superfamily, loss-of-function mutants with reduced cytosolic Hsp70 expression were studied. AtHsp70-1 and AtHsp70-2 are constitutively expressed and represent the major cytosolic Hsp70 isoforms under ambient conditions. Analysis of single and double mutants did not reveal any difference compared to wild-type controls. In yeast, SSE protein has been shown to act as a nucleotide exchange factor, essential for Hsp70 function. To test whether members of the Hsp110/SSE sub-family serve essential functions in plants, two members of the sub-family, AtHsp70-14 and AtHsp70-15, were analysed. Both genes are highly homologous and constitutively expressed. Deficiency of AtHsp70-15 but not of AtHsp70-14 led to severe growth retardation. AtHsp70-15-deficient plants were smaller than wild-type and exhibited a slightly different leaf shape. Stomatal closure under ambient conditions and in response to ABA was impaired in the AtHsp70-15 transgenic plants, but ABA-dependent inhibition of germination was not affected. Heat treatment of AtHsp70-15-deficient plants resulted in drastically increased mortality, indicating that AtHsp70-15 plays an essential role during normal growth and in the heat response of Arabidopsis plants. AtHsp70-15-deficient plants are more tolerant to infection by turnip mosaic virus. Comparative transcriptome analysis revealed that AtHsp70-15-deficient plants display a constitutive stress response similar to the cytosolic protein response. Based on these results, AtHsp70-15 is likely to be a key factor in proper folding of cytosolic proteins, and may function as nucleotide exchange factor as proposed for yeast.
authors.affiliation: Department of Biology, Friedrich Alexander University Erlangen-Nuremberg, Staudtstrasse 5, 91058 Erlangen, Germany.
authors.forename: Isabel
authors.initials: I
authors.lastname: Jungkunz
authors.forename: Katrin
authors.initials: K
authors.lastname: Link
authors.forename: Florian
authors.initials: F
authors.lastname: Vogel
authors.forename: Lars M
authors.initials: LM
authors.lastname: Voll
authors.forename: Sophia
authors.initials: S
authors.lastname: Sonnewald
authors.forename: Uwe
authors.initials: U
authors.lastname: Sonnewald
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D032461:Chromosomes, Plant / Q000235:genetics; D003600:Cytosol / Q000378:metabolism; D020869:Gene Expression Profiling; D055786:Gene Knockout Techniques; D020868:Gene Silencing; D005838:Genotype; D018525:Germination; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D007113:Immunity, Innate; D009154:Mutation; D010641:Phenotype; D010935:Plant Diseases / Q000276:immunology / Q000821:virology; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D017800:Potyvirus / Q000276:immunology / Q000472:pathogenicity; D020033:Protein Isoforms / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D015854:Up-Regulation
chemical_list: D029681:Arabidopsis Proteins; D018840:HSP70 Heat-Shock Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D000040:Abscisic Acid