An aspartic acid protease from common bean is expressed 'on call' during water stress and early recovery

A cDNA encoding a putative aspartic acid protease precursor (PvAP1) was cloned from the leaves of common bean (Phaseolus vulgaris). Sequence analysis showed that PvAP1 presents all the characteristic features of phytepsins, the typical plant APs. PvAP1 gene expression was tightly regulated by water stress, being significantly up-regulated under mild water stress (Ψ(w)=-1.0 MPa) for the drought-susceptible cultivar (Carioca) and moderate water stress (Ψ(w)=-1.5 MPa) for the more drought-tolerant cultivar (IPA). Protein gel blotting analysis under water stress revealed the presence of two main bands of calculated MW of 46 and 38 kDa, suggesting proteolytic processing of the enzyme precursor form under drought in both cultivars. Taken together, our results suggest that water stress regulates PvAP1 activity both at the transcriptional and post-transcriptional levels, and that the response occurs earlier and is stronger in the drought-susceptible cultivar.