Solanum tuberosum aspartic proteases (StAPs) are directly involved in the induction of potato leaves defense response

MUÑOZ, FERNANDO; SASTRE, DIEGO; DALEO, GUSTAVO; GUEVARA, MARÍA

Congreso; XXVIII Reunión Argentina de Fisiología Vegetal.; 2010

Plant aspartic proteases (APs) have been implicated in protein processing and/or degradation in several biological processes. However, a few studies have shown that these proteases are important in plant defense response. We have previously reported the differential expression of Solanum tuberosum aspartic proteases (StAPs) after P. infestans infection, in potato cultivars with different degree of field resistance to this pathogen. The expression of StAPs is higher and more durable in the resistant cultivars than in the susceptible cultivars, and StAPs constitutive expression is detected only in tubers and leaves from resistant cultivars. The aim of this work was to study the role of StAPs in the induction of the potato defense response. Assays were performed using leaves of Bintje cv (susceptible), infiltrated with water or several concentrations of purified StAPs and then, infected with P. infestans. Northern blot analysis confirmed that, after 1.5 h. of StAP infiltration, the increases in the level of NADPH oxidase transcripts were 22, respect to the control. Increases of 9, 2, and 2.5 times were detected in the level of PR1, PotPro and PPI transcripts, after 1.5 h of StAPs infiltration. Results obtained show that, StAP proteolytic activity is necessary to induce the accumulation of NADPH oxidase, PotPro, and PPI transcripts, at all times and concentrations assayed. On the other hand, the size of P. infestans lesion was reduced in a 60 and 40 %, after StAP and StAP-peptatin A infiltration, respectively. Results obtained here suggest that, both activities of StAPs could be involved in the potato resistance to P. infestans: 1-proteolytic activity will be necessary to induce, in a direct or indirect form, the levels of the transcripts of genes involved in plant defense response and consequently, to reduce the colonization of pathogen in the leaves and 2-antimicrobial activity will be necessary to reduce the colonization of the pathogen in the leaves, in a direct form.