CONICET | Buscador de Institutos y Recursos Humanos

Plantdefensins and defensin-like (DEFL) proteins are small basic, cysteine-rich proteinsubiquitously expressed in the plant kingdom and mostly involved in host defence.They present a highly variable sequence but a conserved structure. Sequencediversity appears to be correlated with differential functions exhibited (antifungaland antimicrobial, among others). Two highly conserved regions have beenidentified among plant defensins, which are important for their activity: the g-corelocated in the C-terminal region with a βhairpin structure and the α-corelocated in the N-terminal region. The importance of these motifs lies in the presenceof positive residues which would allow the interaction with negative charges onthe pathogen membrane and/orcell wall. In this work, potential antifungalpeptides were designed from these regions, through the use of bioinformatictools and using as template the sequence of two defensins (DefSm1D and DefSm2)of Silybum marianum previously clonedfrom thistle flowers. Five peptides were synthesized, from DefSm1D sequence:3243, 3245 and 3246; and from DefSm2:3248 and 3250. Then, peptides werepurified and characterized by HPLC-RP, MALDI-TOF-MS and CD. Their activityagainst the phytopathogenic fungus Fusariumgraminearum, their surface-active properties, as well as the ability toexclude the membrane-impermeable dye propidium iodide (PI) of conidia aftertreatment with the peptides were assessed. Peptides 3248 and 3250 were activeagainst F. graminearum at micromolarconcentration and produced PI uptake on conidia. The present work contributesto the knowledge of defensins, which are defense cysteine-rich proteins presentin S. marianum flowers, which grows in Argentina as a wild weed naturallyresistance to fungal pathogens.