The PvSR1(Phaseolus vulgaris stress-related protein) gene encoding an 11 kD proline-rich protein (PRP) was constitutively expansed in the primary leaf tissue of beau (Phaeolus vulgaris L. cv. Saxa). The coarse studies of mRNA accumulation of the PvSR1 has been studied in this plant against virus infection and various abiotic sacsses. Northern blot analysis revealed that the gene expression of PvSR1 was greatly enhanced in the leaf tissue by AIMV (alfalfa mosaic vims) infection, wounding, heat shock, UV, drought and salt stress. The PvSR1 transcripts could also be increased by the exogenous inducing fartors such as salicylic acid and H2O2. The Precise biological roles of PvSR1 is unknown, but the expression of PvSR1 genes in various form of stress suggest that PvSR1 may play an important role during the strees, in maintaining cellular integrity by forming strong linkages with the cell wall.
Using differential screening of a leaf cDNA library prepared from a bean cultivar ( Phaseolus vulgaris L. cv. Saxa) exposed to HgCl 2, the authors have isolated and characterized two heavy metal_regulated cDNA fragments, designated as PvSR 5 and PvSR 51 ( Phaseolus vulgaris stress_related gene). The sequences of the cDNA inserts and homological analysis showed that both PvSR 5 and PvSR 51 encode a polyubiquitin respectively. The polyubiquitin genes were constitutively expressed in roots but weakly expressed in stems and leaves. Northern blot analysis revealed a low level of transcripts of polyubiquitin in unstressed bean leaves, but the gene expression was strongly stimulated by heavy metals, elevated temperature and salicylic acid, whereas wounding had almost no effect. These suggested that polyubiquitin might play important roles in resistance to heavy metals and various environmental stresses.
