eptides Derived From the α-Core and γ-Core Regions of a Putative Silybum marianum Flower Defensin Show Antifungal Activity Against Fusarium graminearum

FERNANDEZ, A.; COLOMBO, M. L; CURTO, L.; GOMEZ, G.; DELFINO, J.; GUZMÁN QUIMBAYO, F.; BAKAS, L; MALBRÁN, I.; VAIRO CAVALLI,S.

Frontiers in Microbiology

Frontiers

Lugar: Lausanne; Año: 2021 vol. 12 p. 155 - 169

1664-302X

Fusarium graminearum is the etiological agent of Fusarium head blight (FHB), a disease thatproduces a significant decrease in wheat crop yield and it is further aggravated by the presence of mycotoxins in the affected grains that may cause in health problems to humans and animals. Plant defensins and defensin-like proteins are antimicrobial peptides; they are small basic, cysteine-rich peptides ubiquitously expressed in the plant kingdom and mostly involved in host defence. Theypresent a highly variable sequence but a conserved structure. The -core located in the C-terminalregion of plant defensins has a conserved β-hairpin structure and is a well-known determinant of the antimicrobial activity among disulphide-containing antimicrobial peptides (AMPs). Anotherconserved motif of plant defensins is the α-core located in the N-terminal region, not conservedamong the disulphide-containing AMPs, it has not been yet extensively studied. In this report, wehave cloned the putative antimicrobial protein DefSm2, expressed in flowers of the wild plant Silybum marianum. The cDNA encodes a protein 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 -core region (SmAP27-44 and SmAP29-35). We have chemically synthesized and purified the peptides and further characterized them by ESI-MS and CD spectroscopy. SmAPα1-21, SmAPα10-21 and SmAP27-44 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 in fungal cell killing. Furthermore, conidia treated for 0.5 h showed cytoplasmic disorganization as observed by TEM. Remarkably, the peptides derived from the α-core induced morphological changes on the conidia cell wall, which is a promising target since its distinctive biochemical and structural organization is absent in plant and mammalian cells.