Expression Analysis of Polyubiquitin Genes from Bean in Response to Heavy Metals

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.