A Heat Shock Protein Gene, CsHsp45.9, Involved in the Response to Diverse Stresses in Cucumber

Heat shock proteins (Hsps) are a family of highly conserved proteins present in all organisms. They mediate a range of cytoprotective functions as molecular chaperones and are recently reported to regulate the immune response. Using suppression subtractive hybridization, we isolated and characterized a cucumber cDNA, designated CsHsp45.9, which encodes a putative heat shock protein of 45.9 kDa protein, containing three conserved DnaJ domains belonging to the Type I Hsp40 family. Real-time quantitative RT-PCR analysis revealed that CsHsp45.9 was significantly induced in cucumber leaves inoculated with downy mildew (Pseudoperonospora cubensis) in this incompatible interaction. Gene expression was also strongly up-regulated by various abiotic stresses. CsHsp45.9 was mainly expressed in flowers with a flower-specific, stamen- and pistil-predominant expression pattern. This suggests that CsHsp45.9 harbors broad-spectrum responses to both biotic and abiotic stresses and may play a role in downy mildew resistance in cucumber.