Structure of Fungal α Mating Pheromone in Membrane Mimetics Suggests a Possible Role for Regulation at the Water-Membrane Interface

Sex Pheromone Receptor Ste2 Orchestrates Chemotropic Growth towards Pine Root Extracts in the Pitch Canker Pathogen Fusarium circinatum

In ascomycetous fungi, sexual mate recognition requires interaction of the Ste2 receptor protein produced by one partner with the α-factor peptide pheromone produced by the other partner. In some fungi, Ste2 is further needed for chemotropism towards plant roots to allow for subsequent infection and colonization. Here, we investigated whether this is also true for the pine pitch canker fungus, Fusarium circinatum, which is a devastating pathogen of pine globally. Ste2 knockout mutants were generated for two opposite mating-type isolates, after which all strains were subjected to chemotropism assays involving exudates from pine seedling roots and synthetic α-factor pheromone, as well as a range of other compounds for comparison. Our data show that Ste2 is not required for chemotropism towards any of these other compounds, but, in both wild-type strains, Ste2 deletion resulted in the loss of chemotropism towards pine root exudate. Also, irrespective of mating type, both wild-type strains displayed positive chemotropism towards α-factor pheromone, which was substantially reduced in the deletion mutants and not the complementation mutants. Taken together, these findings suggest that Ste2 likely has a key role during the infection of pine roots in production nurseries. Our study also provides a strong foundation for exploring the role of self-produced and mate-produced α-factor pheromone in the growth and overall biology of the pitch canker pathogen.

Various Biomimetics, Including Peptides as Antifungals

Biomimetics, which are similar to natural compounds that play an important role in the metabolism, manifestation of functional activity and reproduction of various fungi, have a pronounced attraction in the current search for new effective antifungals. Actual trends in the development of this area of research indicate that unnatural amino acids can be used as such biomimetics, including those containing halogen atoms; compounds similar to nitrogenous bases embedded in the nucleic acids synthesized by fungi; peptides imitating fungal analogs; molecules similar to natural substrates of numerous fungal enzymes and quorum-sensing signaling molecules of fungi and yeast, etc. Most parts of this review are devoted to the analysis of semi-synthetic and synthetic antifungal peptides and their targets of action. This review is aimed at combining and systematizing the current scientific information accumulating in this area of research, developing various antifungals with an assessment of the effectiveness of the created biomimetics and the possibility of combining them with other antimicrobial substances to reduce cell resistance and improve antifungal effects.

α-Pheromone Precursor Protein Foc4-PP1 Is Essential for the Full Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4

Fusarium oxysporum f. sp. cubense (Foc), which causes Fusarium wilt of bananas, is considered one of the most destructive fungal pathogens of banana crops worldwide. During infection, Foc secretes many different proteins which promote its colonization of plant tissues. Although F. oxysporum has no sexual cycle, it has been reported to secrete an α-pheromone, which acts as a growth regulator, chemoattractant, and quorum-sensing signaling molecule; and to encode a putative protein with the hallmarks of fungal α-pheromone precursors. In this study, we identified an ortholog of the α-pheromone precursor gene, Foc4-PP1, in Foc tropical race 4 (TR4), and showed that it was necessary for the growth and virulence of Foc TR4. Foc4-PP1 deletion from the Foc TR4 genome resulted in decreased fungal growth, increased sensitivity to oxidative stress and cell-wall-damaging agents, and attenuation of pathogen virulence towards banana plantlets. Subcellular localization analysis revealed that Foc4-PP1 was concentrated in the nuclei and cytoplasm of Nicotiana benthamiana cells, where it could suppress BAX-induced programmed cell death. In conclusion, these findings suggest that Foc4-PP1 contributes to Foc TR4 virulence by promoting hyphal growth and abiotic stress resistance and inhibiting the immune defense responses of host plants.

Tachyplesin I and its derivatives: A pharmaco-chemical perspective on their antimicrobial and antitumor potential

INTRODUCTION

Increasing evidence suggests that intratumor microbiota are an intrinsic component in the tumor microenvironment across multiple cancer types, and that there is a close relationship between microbiota and tumor progression. Therefore, how to address the interaction between bacteria and malignances has become a growing concern. Tachyplesin I (TPI), a peptide with dual antimicrobial and antitumor effects, holds great promise as a therapeutic alternative for the aforementioned diseases, with the advantage of broad-spectrum activities, quick killing efficacy, and a low tendency to induce resistance.

AREAS COVERED

This review comprehensively summarizes the pharmacological mechanisms of TPI with an emphasis on its antimicrobial and antitumor potential. Furthermore, it presents advances in TPI derivatives and gives a perspective on their future development. The article is based on literature searches using PubMed and SciFinder to retrieve the most up-to-date information of TPI.

EXPERT OPINION

Bacterial infections and cancer both pose a serious threat to health due to their symbiotic interactions and drug resistance. TPI is anticipated to be a novel agent to control pathogenic bacteria and various tumors through multiple mechanisms of action. Indeed, the continuous advancements in chemical modification and innovative applications of TPI give hope for future improvements in therapeutic efficacy.

Chemotropism Assays for Plant Symbiosis and Mycoparasitism Related Compound Screening in Trichoderma atroviride

Trichoderma atroviride is a mycoparasitic fungus used as biological control agent to protect plants against fungal pathogens. Successful biocontrol is based on the perception of signals derived from both the plant symbiont and the fungal prey. Here, we applied three different chemotropic assays to study the chemosensing capacity of T. atroviride toward compounds known or suspected to play a role in the mycoparasite/plant or host/prey fungal interactions and to cover the complete spectrum of T. atroviride developmental stages. Purified compounds, including nutrients, the fungal secondary metabolite 6-amyl-α-pyrone (6-pentyl-α-pyrone, 6-PP) and the plant oxylipin 13-(s)-HODE, as well as culture supernatants derived from fungal preys, including Rhizoctonia solani, Botrytis cinerea and Fusarium oxysporum, were used to evaluate chemotropic responses of conidial germlings, microcolonies and fully differentiated mycelia. Our results show that germlings respond preferentially to compounds secreted by plant roots and T. atroviride itself than to compounds secreted by prey fungi. With the progression of colony development, host plant cues and self-generated signaling compounds remained the strongest chemoattractants. Nevertheless, mature hyphae responded differentially to certain prey-derived signals. Depending on the fungal prey species, chemotropic responses resulted in either increased or decreased directional colony extension and hyphal density at the colony periphery closest to the test compound source. Together these findings suggest that chemotropic sensing during germling development is focused on plant association and colony network formation, while fungal prey recognition develops later in mature hyphae of fully differentiated mycelium. Furthermore, the morphological alterations of T. atroviride in response to plant host and fungal prey compounds suggest the presence of both positive and negative chemotropism. The presented assays will be useful for screening of candidate compounds, and for evaluating their impact on the developmental spectrum of T. atroviride and other related species alike. Conidial germlings proved particularly useful for simple and rapid compound screening, whereas more elaborate microscopic analysis of microcolonies and fully differentiated mycelia was essential to understand process-specific responses, such as plant symbiosis and biocontrol.