Programmed cell death (PCD) occurs in plants, animals and several branches of unicellular eukaryotes as a part of developmental and/or defense processes.
Caspase proteases are universal mediators of animal apoptosis, a type of PCD. In plants, there are not animal
caspase homologs; therefore, the characterization of
caspase-like activities is of considerable importance to our understanding of PCD in plants. Here we report for the first time the involvement of caspase-3-like activity in the resistance mechanism of potato to Phytophthora infestans
infection. We showed that disease development in infected potato leaves is dependent of caspase-3-like activity. Unlike plant DEVDases previously reported, this
DEVDase activity was sensitive to the
serine protease inhibitor PMSF. As reported for other
subtilisin- like
proteases with
caspase activity, potato
DEVDase activity was mainly localized in the apoplast. We demonstrated that in total
protein extract
DEVDase activity accounts for a 60% of
serine proteases; however, this percentage increases to 100% in the apoplast. Additionally, this caspase-3-like activity is constitutively expressed in the apoplast of potato leaves. Total
DEVDase activity is induced only in potato cultivars with high field resistance to P. infestans. These results show that potato caspase-3-like
protease could constitute a tool in the potato defense mechanisms resulting in partial resistance, although further assays would be necessary in order to elucidate its role.