Peptides derived from the alpha and gamma-core regions of a putative Silybum marianum flower defensin show antifungal activity against Fusarium graminearum

FERNÁNDEZ, AGUSTINA; COLOMBO, MARÍA LAURA; CURTO, LUCRECIA MARÍA; GÓMEZ, GABRIELA ELENA; DELFINO, JOSÉ MARÍA; GUZMÁN, FANNY; BAKÁS, LAURA; MALBRÁN, ISMAEL; VAIRO CAVALLI, SANDRA

Frontiers in Microbiology

Frontiers Media SA

Año: 2021

1664-302X

Plant defensins and defensin-like (DEFL) proteins are antimicrobial peptides (AMPs), they are small basic, cysteine-rich peptides (CRPs) ubiquitously expressed in the plant kingdom and mostly involved in host defence. They present a highly variable sequence but a conserved structure. Two conserved regions have been reported as relevant for their activity, the γ-core located in the C-terminal region with a β-hairpin structure and the α-core located in the N-terminal region. In this study, we have cloned the putative antimicrobial protein DefSm2, expressed in flowers of the wild plant Silybum marianum. The cDNA encodes a protein of 95 aminoacids with two fused basic domains of an N-terminal defensin domain (DefSm2-D) and a C-terminal Arg- and Lys-rich domain. To further characterize the DefSm2-D domain, we built a 3D template-based model that will serve to support the design of novel antifungal peptides. We have designed four potential antifungal peptides, two from the DefSm2-D α-core region (SmAPα1-21 and SmAPα10-21) and two from the γ-core region (SmAPγ27-44 and SmAPγ29-35). We have chemically synthesized and purified the peptides and further characterized them by ESI-MS and CD spectroscopy. SmAPα1-21, SmAPα10-21 and SmAPγ27-44 inhibited the growth of the phytopathogen Fusarium graminearum at low micromolar concentrations. Conidia exposure to the fungicidal concentration of the peptides caused membrane permeabilization to the fluorescent probe propidium iodide (PI), suggesting that this is one of the main contributing factors for the fungal cell killing. Poner algo sobre la desorganización citoplasmática en los conidios con 30 minutos de tratamiento, según lo observado en el TEM. Remarkably, the peptides derived from the α-core induced morphological changes on the conidia cell wall, a promising target since its distinctive biochemical and structural organization is absent in plant and mammalian cells.