Ismael Malbrán

Background: The use of antimicrobial peptides (AMPs) as biotechnological tools is an area of growing interest in the research that seeks to improve crop defense. SmAP_α1–21 and SmAP_γ27–44 were previously reported to inhibit Fusarium graminearum, permeabilize the plasma membrane and induce cytoplasmic disorganization. To exert its activity, SmAP_α1–21 initially enters through the basal and apical cells of F. graminearum conidia and then displays a general but non-homogeneous distribution in the cytoplasm of all conidial cells, in contrast. Methods: We analyzed, focusing on membrane interaction, the mode of action of SmAP_γ27–44, a peptide based on the γ-core of defensins DefSm2-D and DefSm3, and SmAP_α1–21, based on the α-core of DefSm2-D. Additionally, we compared the behavior of SmAP_α1–21 with that of SmAP3_α1–21 based on DefSm3 but with no activity against F. graminearum. Results: In this study, we showed that SmAP_γ27–44 enters the cells with discrete intracellular localization. Furthermore, both peptides disrupted the plasma membrane, but with different modes of action. When large unilamellar liposomes (LUVs) containing phosphatidic acid and ergosterol were used as a filamentous fungal plasma membrane model, SmAP_γ27–44 strongly induced aggregation concomitantly with the solubilization of the liposomes and showed the maximal insertion of its tryptophan moiety into the membrane’s hydrophobic interior. In comparison, SmAP_α1–21 showed a high effect on the ζ potential of anionic vesicles, vesicle aggregation capacity after reaching a concentration threshold, and moderate transfer of tryptophan to the membrane. SmAP3_α1–21, on the other hand, showed poor superficial adsorption to liposomes. Conclusions: In view of our results, a cell penetration peptide-like effect was pictured for the γ-core defensin-derived peptide and a classical AMP action was observed for the α-core defensin-derived one.

The synthetic peptide SmAP_α1-21 (KLCEKPSKTWFGNCGNPRHCG) derived from DefSm2-D defensin α-core is active at micromolar concentrations against the phytopathogenic fungus Fusarium graminearum and has a multistep mechanism of action that includes alteration of the fungal cell wall and membrane permeabilization. Here, we continued the study of this peptide’s mode of action and explored the correlation between the biological activity and its primary structure. Transmission electron microscopy was used to study the ultrastructural effects of SmAP_α1-21 in conidial cells. New peptides were designed by modifying the parent peptide SmAP_α1-21 (SmAPH19R and SmAPH19A, where His19 was replaced by Arg or Ala, respectively) and synthesized by the Fmoc solid phase method. Antifungal activity was determined against F. graminearum. Membrane permeability and subcellular localization in conidia were studied by confocal laser scanning microscopy (CLSM). Reactive oxygen species (ROS) production was assessed by fluorescence spectroscopy and CLSM. SmAP_α1-21 induced peroxisome biogenesis and oxidative stress through ROS production in F. graminearum and was internalized into the conidial cells’ cytoplasm. SmAPH19R and SmAPH19A were active against F. graminearum with minimal inhibitory concentrations (MICs) of 38 and 100 µM for SmAPH19R and SmAPH19A, respectively. The replacement of His19 by Ala produced a decrease in the net charge with a significant increase in the MIC, thus evidencing the importance of the positive charge in position 19 of the antifungal peptide. Like SmAP_α1-21, SmAP2H19A and SmAP2H19R produced the permeabilization of the conidia membrane and induced oxidative stress through ROS production. However, SmAPH19R and SmAPH19A were localized in the conidia cell wall. The replacement of His19 by Ala turned all the processes slower. The extracellular localization of peptides SmAPH19R and SmAPH19A highlights the role of the His19 residue in the internalization.

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum (Schwabe), is a destructive disease worldwide, reducing wheat yield and quality. To accelerate the improvement of scab tolerance in wheat, we assessed the International Triticeae Mapping Initiative mapping population (ITMI/MP) for Type I and II resistance against a wide population of Argentinean isolates of F. graminearum. We discovered a total of 27 additive QTLs on ten different (2A, 2D, 3B, 3D, 4B, 4D, 5A, 5B, 5D and 6D) wheat chromosomes for Type I and Type II resistances explaining a maximum of 15.99% variation. Another four and two QTLs for thousand kernel weight in control and for Type II resistance, respectively, involved five different chromosomes (1B, 2D, 6A, 6D and 7D). Furthermore, three, three and five QTLs for kernel weight per spike in control, for Type I resistance and for Type II resistance, correspondingly, involved ten chromosomes (2A, 2D, 3B, 4A, 5A, 5B, 6B, 7A, 7B, 7D). We were also able to detect five and two epistasis pairs of QTLs for Type I and Type II resistance, respectively, in addition to additive QTLs that evidenced that FHB resistance in wheat is controlled by a complex network of additive and epistasis QTLs.

Several Fusarium species cause disease on human hosts, including commonly fatal infections in immunocompromised individuals. Recently, cases of hospitalized patients affected by fusaria were reported in the Tyrrhenian Island of Sardinia, Italy. To precisely characterize the Fusarium species and haplotypes present in hospitals of the region, a multilocus DNA sequence typing (MLST) approach was applied. Water distribution systems in four departments belonging to four Sardinian hospitals were sampled. Fusarium species and sequence types (STs) were identified using MLST based on sequences of the elongation factor 1-alpha (EF-1α) gene, the nuclear ribosomal DNA intergenic spacer region (IGS rDNA), and/or a portion of the second-largest subunit of RNA polymerase (RPB2) gene. The majority of isolates obtained from Sardinian hospitals (90.7%) were identified as representatives of the Fusarium oxysporum species complex (FOSC), followed by those of the F. solani species complex (FSSC) (8.2%), and F. dimerum (1.1% of all isolates). Ten STs were found among the FOSC and FSSC, with more than 60% of the isolates identified as either FOSC ST 33 or FSSC 1 (F. petroliphilum). More than half of the FOSC isolates obtained from the water systems in all four hospitals belonged to the worldwide distributed clonal lineage ST 33. This haplotype is the most prevalent among the FOSC in different countries, being responsible for the vast majority of cases of human fusariosis.

More than 15,000 ha of tomato (Solanum lycopersicum L.) are annually cultivated under greenhouse and field conditions in Argentina. From December 2013 to December 2016, plants of cultivar ‘Elpida’ ...

Bacteria promote growth by different mechanisms like phosphate (Pi) solubilization, Indol Acetic Acid (IAA) synthesis and siderophores production. The purpose of this study was to isolate bacteria that promote the growth of plants and may also act as antagonistic organisms of plant pathogens. Pi solubilizing microorganisms that were isolated from the soils of Tres Arroyos, Buenos Aires; were also able to synthesize IAA and produce siderophores. The ability of these bacteria to solubilize Pi was directly related with the synthesis of organic acids that lowered the pH and was not related with phosphatase activity. The ability of the organisms to solubilize Pi was indirectly related with the amount of soluble Pi present in the media. Though Pi solubilizing microorganisms are mainly associated with the rhizoplane exudates, in this case did not induce Pi solubilization. In addition to promote plant growth, these bacteria proved to be antagonistic of plant pathogens such as Fusarium graminearum and F. solani.

Objectives: Differences in aggressiveness and mycotoxin production were previously found among isolates of Fusarium graminearum, the main incitant of Fusarium head blight (FHB) of wheat, from Argentina. This study aims at evaluating the genetic diversity present in these isolates and its relationship with their aggressiveness. Methods: inter-simple sequence repeats polymerase chain reaction (ISSR-PCR) was used to asses the genetic variability present in 112 F. graminearum isolates from 28 localities of Buenos Aires Province, Argentina. The analysis of molecular variance (AMOVA) was performed to examine the population structure. Results: F. graminearum populations from Argentina showed a large genotypic variability. Seventy seven percent of the isolates included in the analysis were identified as a unique haplotype. The largest part of this variation resulted from genetic differences within (89%) rather than between populations (11%). The constructed dendrogram showed no genotype clustering according to geographic origin or aggressiveness of the isolates. Conclusions: a high genetic heterogeneity was found in the F. graminearum populations from Argentina. This diversity can possibly reflect the occurrence of high frequencies of sexual outcrosses in the field and gene flow.

Tomato (Solanum lycopersicum L.) is among the most important horticultural crops in Argentina. The green belt area surrounding the city of La Plata (Buenos Aires, Argentina) represents around 30% of the horticultural production of the province. Annually, an average of 408 hectares of tomato is harvested in this region, of which 70% is for fresh consumption and 30% for processing. During the summer 2013/2014, postharvest fruit rot was found in 20% of the many storage facilities from the horticultural area of La Plata on fresh market tomatoes fruits cv. Elpida. Symptoms started as small circular lesions of watery aspect that increased in size over time. Lesions destroyed subepidermal tissue causing ruptures in the epidermis and the emergence of abundant white mycelium. Fruits would eventually collapse. Surface disinfested pieces of symptomatic fruit were placed on potato dextrose agar (PDA) medium and incubated at 23 ± 2°C with a cycle of 12 hrs of light/12 hrs of dark for 9 days in a growth chamber. Fusari...