Evidence for non-circadian light/dark-regulated expression of Hsp70s in spinach leaves.
Expression of six Hsp70s in spinach (Spinacia oleracea cv Longstanding Bloomsdale) leaves grown under isothermal conditions is regulated by a light/dark (L/D) mechanism distinctly different from the light-regulated mechanism for the chlorophyll a/b-binding protein (cab) or small subunit of ribulose-1,5-bisphosphate carboxylase oxygenase (rbcS). Subjecting entrained plants to two or three L/D cycles within a 24-h period resulted in an equal number of oscillations in expression for five out of six 70-kD heat shock proteins (Hsp70s). Three cycles appear to be the maximum, as shorter L/D treatments do not consistently increase the number of cycles in a 24-h period. The expression response of Hsp70s to L/D is overridden by heat shock. Protein disulfide isomerase, a second molecular chaperone of the endoplasmic reticulum, has an expression pattern in entrained plants that is similar to hsc70-2, the endoplasmic reticulum luminal Hsp70 binding protein. The parallel expression patterns for the various Hsp70s and protein disulfide isomerase indicate a likely general coordinate L/D regulation for molecular chaperones in plants. Multiple inductions in response to successive L/D treatments within a 24-h period in entrained plants for five of six Hsp70s support the conclusion that expression is not a consequence of circadian control, but instead is independently cued by non-circadian-mediated L/D signals where peak Hsp70 expression precedes the daily thermoperiod maximum.
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Plant Molecular and Cellular Biology Program, Department of Environmental Horticulture, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611-0670, USA.
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D001683:Biological Clocks; D002940:Circadian Rhythm; D003624:Darkness; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010507:Periodicity; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics; D018515:Plant Leaves / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics; D018724:Spinacia oleracea / Q000235:genetics / Q000502:physiology*
D018840:HSP70 Heat-Shock Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D020033:Protein Isoforms; D012273:Ribulose-Bisphosphate Carboxylase