A full-length cDNA denominated PvP5CS for Delta(1)-pyrroline-5-carboxylate synthetase (P5CS), an enzyme involved in the biosynthesis of proline, was cloned from common bean using a candidate gene approach. PvP5CS contains an open reading frame encoding a 716 amino acid polypeptide. Sequence analysis showed that PvP5CS shares 95.1% homology in nucleotide sequence and 93.2% identity in amino acid sequence with the mothbean (Vigna aconitifolia) P5CS. The expression patterns of PvP5CS in common bean treated with drought, cold (4 degrees C), and salt (200 mM NaCl) stresses were examined using real-time quantitative PCR. These abiotic stresses caused significant up-regulation of the expression of PvP5CS in leaves. The PvP5CS mRNA transcript increased to 2.5 times the control level after 4d drought stress. A rapid up-regulation of PvP5CS, to about 16.3 times the control at 2h post-treatment was observed under salt stress. A significant increase in PvP5CS expression (11.7-fold) was detected after 2h of cold stress. The peaks of proline accumulation appeared at 8d for drought, 24h for cold and 9h for salt stress, somewhat later than the peaks of PvP5CS expression. These results suggest that PvP5CS was a stress-inducible gene regulating the accumulation of proline in plants subjected to stress. Finally, subcellular localization assays showed that the PvP5CS protein was present in the nucleus and at the plasmalemma.