title: Interplay between circadian rhythm, time of the day and osmotic stress constraints in the regulation of the expression of a Solanum Double B-box gene.
abstract: OBJECTIVE
  Double B-box zinc finger (DBB) proteins are recently identified plant transcription regulators that participate in the response to sodium chloride-induced stress in arabidopsis plants. Little is known regarding their subcellular localization and expression patterns, particularly in relation to other osmotic constraints and the day/night cycle. This study investigated natural variations in the amount of a Solanum DBB protein, SsBBX24, during plant development, and also under various environmental constraints leading to cell dehydration in relation to the circadian clock and the time of day.
  
  
  METHODS
  SsBBX24 transcript and protein abundance in various organs of phytotron-grown Solanum tuberosum and S. sogarandinum plants were investigated at different time points of the day and under various osmotic constraints. The intracellular location of SsBBX24 was determined by western blot analysis of subcellular fractions.
  
  
  RESULTS
  Western blot analysis of SsBBX24 protein revealed that it was located in the nucleus at the beginning of the light period and in the cytosol at the end, suggesting movement ('trafficking') during the light phase. SsBBX24 gene expression exhibited circadian cycling under control conditions, with the highest and lowest abundances of both transcript and protein occurring 8 and 18 h after dawn, respectively. Exposing Solanum plants to low temperature, salinity and polyethylene glycol (PEG), but not to drought, disturbed the circadian regulation of SsBBX24 gene expression at the protein level. SsBBX24 transcript and protein accumulated in Solanum plants in response to salt and PEG treatments, but not in response to low temperature or water deficit. Most interestingly, the time of the day modulated the magnitude of SsBBX24 expression in response to high salt concentration.
  
  
  CONCLUSIONS
  The interplay between circadian rhythm and osmotic constraints in the regulation of the expression of a Solanum DBB transcriptional regulator is demonstrated. It is proposed that stress-dependent, post-transcriptional mechanisms alter the regulation by the circadian clock of the amount of SsBBX24.
authors.affiliation: Institute of Plant Genetics, Polish Academy of Sciences, Strzeszyńska 34, 60-479 Poznań, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Kiełbowicz-Matuk
authors.forename: Pascal
authors.initials: P
authors.lastname: Rey
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Rorat
mesh_terms: D000595:Amino Acid Sequence; D002940:Circadian Rhythm; D003080:Cold Temperature; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D032322:Solanum / Q000235:genetics* / Q000378:metabolism; D011198:Solanum tuberosum / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D012097:Repressor Proteins
keywords: Circadian clock; Double B-box protein; Solanum sogarandinum; Solanum tuberosum; gating; osmotic stress; salinity