Wheat defense against the disease caused by Septoria tritici. The degradation of specific proteins of conidiospores by leaf extracellular proteases.

SEGARRA, C.; MANSILLA, A.; CASALONGUE, C; CORDO, C.; CONDE, R.

Mar del Plata - Buenos Aires - Argentina

Congreso; Seventh International Wheat Congress; 2005

INTA - S.A.G.P.y A.

We found previously that the intercellular fluid of wheat leaf contains a serine protease activity mainly constituted by two isoforms (Pinedo et al., 1993). This activity changes according to the resistance of cultivars to the attack of the pathogenic fungus Septoria tritici. Thus, 10-12 days after the inoculation of plants with S. tritici, it increases 4 times in the resistant cv. Pigüé and decreases lightly in the susceptible cv. Isla Verde. Next, we observed that the conidiospores of S. tritici do not germinate when are incubated during 24 h with the apoplastic serine protease activity.  These results suggested that the aforementioned activity participates in the defense of wheat plants against the attack of S. tritici (Segarra et al., 2002). Even though there are numerous families of proteins that present antifungal activity (PR 1, PR 2, PR 3, PR 4, PR 5, defensins, cyclophilin like proteins, glycine-histidine rich proteins; Selitrennikoff, 2001), their mechanisms of action are scarcely known. In order to advance in the knowledge of the mechanism that determines the antifungal capability of the protease activity, its action on the proteins of S. tritici conidiospores was examined. By means of SDS-PAGE, there were recognized four degraded proteins whose relative molecular masses were 86.4, 59.8, 44.4, and 37.2 kDa. The subsequent identification of these proteins would constitute a significant advance to comprehend the defense mechanism of wheat plants against S. tritici.