rHsp90 gene expression in response to several environmental stresses in rice (Oryza sativa L.)

In this study, the gene for a rice (Oryza sativa L.) 90 kDa heat shock protein (rHsp90, GenBank accession no. AB037681) was identified by screening rice root cDNAs that were up-regulated under carbonate (NaHCO3) stress using the method of differential display, and cloned. The open-reading-frame of rHsp90-cDNA was predicted to encode a protein containing 810 amino acids, which showed high similarity to proteins in Hordeum vulgare (accession no. X67960) and Catharathus roseus (accession no. L14594). Further studies showed that rHsp90 mRNA accumulated following exposure to several abiotic stresses, including salts (NaCl, NaHCO3 and Na2CO3), desiccation (using polyethylene glycol), high pH (8.0 and 11.0) and high temperature (42 and 50 °C). Yeast (Saccharomyces cerevisiae) over-expressing rHsp90 exhibited greater tolerance to NaCl, Na2CO3 and NaHCO3 and tobacco seedlings over-expressing rHsp90 could tolerate salt concentrations as high as 200 mM NaCl, whereas untransformed control seedlings couldnʹt. These results suggest that rHsp90 plays an important role in multiple environmental stresses.