Cloning and expression analysis of the heavy-metal responsive gene PvSR2 from bean

A heavy metal responsive gene PvSR2 (Phaseolus vulgaris stress related) whi ch encodes a new heavy metal stress related protein was isolated from a mer curic-chloride-treated bean (Phaseolus vulgaris L.) cDNA library by differe ntial screening using cDNAs derived from treated and untreated plants. The PvSR2 cDNA contains 690 bp, which is about 200 bp shorter than the full len gth mRNA. Genomic DNA clone sequence analysis showed that PvSR2 gene contai ns no introns in the coding region. The deduced protein with a calculated m olecular weight of 18.5 kDa. The cDNA and protein sequence of PvSR2 has no homology with any known protein. A single copy of PvSR2 was found in bean g enomic DNA by Southern blot analysis. Northern blot analysis revealed that PvSR2 mRNA is hardly detectable in unstressed bean seedlings. The gene expr ession was strongly stimulated by heavy metals, such as mercury, cadmium, a rsenic and copper, whereas it was not responsive to any other forms of envi ronment stresses, such as ultraviolet radiation, elevated temperature and v irus infection. PvSR2 gene was cloned into a prokaryotic expression vector pBV221 with a PRPL promoter upstream. The heavy metal resistance assay of E coli DH5 alpha strain showed that the transformant DH5a of pBV221-PvSR2 re combinant plasmid displayed obviously resistance to CdCl2 compared with the transformant of pBV221 plasmid (negative control) and the DH5 alpha (contr ol). These suggested that the PvSR2 is a specific heavy metal responsive ge ne and might play an important role in resistance to the damage caused by h eavy metals. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.