title: Ecotypic variation in chloroplast small heat-shock proteins and related thermotolerance in Chenopodium album.
abstract: Production of chloroplast-localized small heat-shock proteins (Cp-sHSP) is correlated with increased thermotolerance in plants. Ecotypic variation in function and expression of Cp-sHSPs was analyzed in two Chenopodium album ecotypes from cool vs. warm-temperate USA habitats [New York (NY) and Mississippi (MS) respectively]. P(et) was more heat tolerant in the MS than the NY ecotype, and MS ecotype derived proportionally greater protection of P(et) by Cp-sHSP during high temperatures. Four genes encoding Cp-sHSPs were isolated and characterized: CaHSP25.99n (NY-1) and CaHSP26.23n (NY-2) from NY ecotype, and CaHSP26.04m (MS-1) and CaHSP26.26m (MS-2) from MS ecotype. The genes were nearly identical in predicted amino-acid sequence and hydrophobicity. Gene expression analysis indicated that MS-1 and MS-2 transcripts were constitutively expressed at low levels at 25 °C, while no NY-1 and NY-2 transcripts were detected at this temperature. Maximum accumulation of NY-1 and NY-2 transcripts occurred at 33 °C and 40 °C for MS-1 and MS-2. Immunoblot analysis revealed that (1) protein expression was highest at 37 °C in both ecotypes, but was greater in MS than NY ecotype at 40 °C; and (2) import of Cp-sHSP into chloroplasts was more heat-labile in NY ecotype. The higher expression of one isoform in MS ecotype may contribute to its enhanced thermotolerance. Absence of correlation between protein and transcript levels, suggests the post-transcriptional regulation is occurring. Promoter analysis of these genes revealed significant variations in heat-shock elements (HSE), core motifs required for heat-shock-factor binding. We propose a correlation between unique promoter architecture, Cp-sHSP expression and thermotolerance in both ecotypes.
authors.affiliation: Department of Biochemistry, and Molecular Biology, Mississippi State University, MS, USA. snq@qau.edu.pk
authors.forename: Samina
authors.initials: S
authors.lastname: Shakeel
authors.forename: Noor Ul
authors.initials: NU
authors.lastname: Haq
authors.forename: Scott A
authors.initials: SA
authors.lastname: Heckathorn
authors.forename: E William
authors.initials: EW
authors.lastname: Hamilton
authors.forename: Dawn S
authors.initials: DS
authors.lastname: Luthe
mesh_terms: D020121:5' Untranslated Regions; D001483:Base Sequence; D027463:Chenopodium album / Q000235:genetics / Q000502:physiology*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004579:Electron Transport; D018506:Gene Expression Regulation, Plant; D050888:Heat-Shock Proteins, Small / Q000235:genetics* / Q000378:metabolism; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D008922:Mississippi; D008969:Molecular Sequence Data; D009518:New York; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D020121:5' Untranslated Regions; D050888:Heat-Shock Proteins, Small; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D020033:Protein Isoforms