Plant defense elicited by a subtilisin-like protease of Acremonium strictum

CHALFOUN, NADIA REGINA; CASTAGNARO, ATILIO P; DÍAZ RICCI, JUAN C.

Mar del Plata

Congreso; 29º Reunión Anual de la Sociedad Argentina de Fisiología Vegetal; 2012

Sociedad Argentina de Fisiología Vegetal

When plants recognize elicitor molecules derived from pathogens activate a complex network of signals that brings about a defensive response to restrict the growth of the pathogen. PAMP triggered immunity (PTI) and effector triggered immunity (ETI) are two of the defense mechanisms induced in plants depending on the type of molecule involved. We have isolated and purified a protein secreted by the fungus Acremonium strictum that induces a strong defensive response against the pathogen Colletotrichum, the etiological agent of the anthracnose disease in strawberry. Biochemical and molecular studies showed that the elicitor is a basic protein (pI 8.8) of 34 kDa that presents a high similarity with fungal serine proteinases of the subfamily S8A of subtilisin. Sequence analysis revealed that the elicitor-encoding cDNA consists in a 1167 nucleotides sequence. Analysis of the deduced aminoacid sequence suggests that elicitor is expressed as a larger precursor, that contains in addition to the 283-residues of mature protein, 15-residue corresponding to a secretory signal peptide and a 90-residue peptidase inhibitor domain I9. The mature protein exhibits proteolytic activity, and is inhibited by PMSF but not by TPCK confirming that the elicitor is a serine-protease of the subtilisin familiy. The elicitation of a defense response was evaluated by analyzing the accumulation of reactive oxygen species (H2O2 and O2.-), callose, salicylic acid and the expression of defense related genes (i.e. Fapr1, Fachi2-1). Results showed that elicitor treated plants acquire resistance to anthracnose, exhibit a rapid accumulation of H2O2 and O2.- with maximum 8 hpt, a slower accumulation of salicylic acid with a maximum 48 hpt, and an increase of callose deposit 7 dpt. The genes Fapr1 and Fachi2-1 also showed upregulation 48 hpt indicating the elicitor can not only activate defense response metabolisms but also the transcription of defense associated genes.