Chitin Synthases from Saprolegnia Are Involved in Tip Growth and Represent a Potential Target for Anti-Oomycete Drugs

Abstract

Oomycetes represent some of the most devastating plant and animal pathogens. Typical examples are Phytophthora infestans, which causes potato and tomato late blight, and Saprolegnia parasitica, responsible for fish diseases. Despite the economical and environmental importance of oomycete diseases, their control is difficult, particularly in the aquaculture industry. Carbohydrate synthases are vital for hyphal growth and represent interesting targets for tackling the pathogens. The existence of 2 different chitin synthase genes (SmChs1 and SmChs2) in Saprolegnia monoica was demonstrated using bioinformatics and molecular biology approaches. The function of SmCHS2 was unequivocally demonstrated by showing its catalytic activity in vitro after expression in Pichia pastoris. The recombinant SmCHS1 protein did not exhibit any activity in vitro, suggesting that it requires other partners or effectors to be active, or that it is involved in a different process than chitin biosynthesis. Both proteins contained N-terminal Microtubule Interacting and Trafficking domains, which have never been reported in any other known carbohydrate synthases. These domains are involved in protein recycling by endocytosis. Enzyme kinetics revealed that Saprolegnia chitin synthases are competitively inhibited by nikkomycin Z and quantitative PCR showed that their expression is higher in presence of the inhibitor. The use of nikkomycin Z combined with microscopy showed that chitin synthases are active essentially at the hyphal tips, which burst in the presence of the inhibitor, leading to cell death. S. parasitica was more sensitive to nikkomycin Z than S. monoica. In conclusion, chitin synthases with species-specific characteristics are involved in tip growth in Saprolegnia species and chitin is vital for the micro-organisms despite its very low abundance in the cell walls. Chitin is most likely synthesized transiently at the apex of the cells before cellulose, the major cell wall component in oomycetes. Our results provide important fundamental information on cell wall biogenesis in economically important species, and demonstrate the potential of targeting oomycete chitin synthases for disease control.

Aphanomyces euteiches Cell Wall Fractions Containing Novel Glucan-Chitosaccharides Induce Defense Genes and Nuclear Calcium Oscillations in the Plant Host Medicago truncatula

“…Heterologous expression and in vitro biochemical assays have revealed that the CHS2 gene from Saprolegnia monoica actually encodes a functional CHS enzyme. The latter is inhibited by nikkomycin Z, a structural analogue of the chitin synthase substrate UDP-GlcNAc, which further supports the occurrence of chitin in this microorganism [16].…”

Analyses of Extracellular Carbohydrates in Oomycetes Unveil the Existence of Three Different Cell Wall Types

“…This is illustrated by the case of pathogenic fungi, for instance, Candida albicans, in which 1,3-␤-glucan biosynthesis can be specifically blocked by drugs from the echinocandin family (10), thereby leading to cell death. In addition, our group has recently demonstrated the potential of targeting the biosynthesis of the minor chitin component in the oomycete Saprolegnia monoica for disease control (11).…”

Clotrimazole as a Potent Agent for Treating the Oomycete Fish Pathogen Saprolegnia parasitica through Inhibition of Sterol 14α-Demethylase (CYP51)

“…Recently, alternate chemical approaches have been tried to control S. parasitica infection with varying success, including chemically modified chitosans (27), peracetic acid (28), saprolmycins (29), oridamycins (30), Pyceze (2-bromo-2-nitropropane-1,3-diol) (12), and essential oils and ethanol extracts of medicinal plants (31). In addition, chitin synthases responsible for tip growth in Saprolegnia have been identified as potential targets for anti-oomycete drugs (32). Effective strategies and chemicals still need to be developed to control or eradicate Saprolegnia infections in aquaculture, especially in freshwater environments, with at least the same efficacy as malachite green.…”