The bean PvSR2 gene produces two transcripts by alternative promoter usage

The bean (Phaseolus vulgaris) stress-related gene number 2 (PvSR2) is heavy metal-inducible. Here, the intron of PvSR2 (I-PvSR) within the coding sequence was isolated and characterized. I-PvSR exhibited a weak and constitutive promoter activity and enhanced the PvSR2 promoter activity in transiently transformed tobacco protoplasts. The transcription start site of I-PvSR promoter was mapped 72 bp upstream of the 3′-splice site. The shorter PvSR2 transcript (768 nt) in bean is generated from this intronic promoter and lacks the last 56 bases of 3′-end sequence of longer PvSR2 transcript (829 nt) by utilizing an alternative polyadenylation site. Quantitative competitive PCR analysis further revealed that two transcripts were differently accumulated in response to Hg2+-exposure and the longer transcript was more abundant than the shorter one. These results demonstrate an additional non-metal inducible transcription of PvSR2 via alternative intronic promoter usage and provide new insights into expression mechanism of metal inducible gene.