Different Chitin Synthase Genes Are Required for Various Developmental and Plant Infection Processes in the Rice Blast Fungus Magnaporthe oryzae

Abstract

Chitin is a major component of fungal cell wall and is synthesized by chitin synthases (Chs). Plant pathogenic fungi normally have multiple chitin synthase genes. To determine their roles in development and pathogenesis, we functionally characterized all seven CHS genes in Magnaporthe oryzae. Three of them, CHS1, CHS6, and CHS7, were found to be important for plant infection. While the chs6 mutant was non-pathogenic, the chs1 and chs7 mutants were significantly reduced in virulence. CHS1 plays a specific role in conidiogenesis, an essential step for natural infection cycle. Most of chs1 conidia had no septum and spore tip mucilage. The chs6 mutant was reduced in hyphal growth and conidiation. It failed to penetrate and grow invasively in plant cells. The two MMD-containing chitin synthase genes, CHS5 and CHS6, have a similar expression pattern. Although deletion of CHS5 had no detectable phenotype, the chs5 chs6 double mutant had more severe defects than the chs6 mutant, indicating that they may have overlapping functions in maintaining polarized growth in vegetative and invasive hyphae. Unlike the other CHS genes, CHS7 has a unique function in appressorium formation. Although it was blocked in appressorium formation by germ tubes on artificial hydrophobic surfaces, the chs7 mutant still produced melanized appressoria by hyphal tips or on plant surfaces, indicating that chitin synthase genes have distinct impacts on appressorium formation by hyphal tip and germ tube. The chs7 mutant also was defective in appressorium penetration and invasive growth. Overall, our results indicate that individual CHS genes play diverse roles in hyphal growth, conidiogenesis, appressorium development, and pathogenesis in M. oryzae, and provided potential new leads in the control of this devastating pathogen by targeting specific chitin synthases.

Modulation of Alternaria infectoria Cell Wall Chitin and Glucan Synthesis by Cell Wall Synthase Inhibitors

“…In the present study, in both of the A. infectoria strains tested, CHSE, a class VII Chs that contain an MMD, was overexpressed in response to caspofungin and nikkomycin Z. Class VII enzymes have also been demonstrated to be essential for virulence in several plant pathogens (21,61) and, together with class V Chs, seem to play a crucial structural role in the human pathogen A. fumigatus and in A. nidulans (62,63).…”

“…This multiplicity of isoforms implies specificity of function, as it occurs in other fungi (21,55). We found that the expression of some CHS genes was altered, depending on the antifungal and on the A. infectoria strain.…”

“…In this major human pathogen, Chs1 and Chs3 are responsible for canonical septum formation while Chs2 and Chs8 account for most of the in vitro chitin synthase activity and are upregulated by echinocandins (6,19,20). Chitin synthases belonging to classes III, V, VI, and VII are distributed only in the genomes of filamentous fungi and dimorphic yeasts that have high chitin contents in their cell walls (21). Class V and VII chitin synthases contain a myosin motor domain (MMD) in their N-terminal region (22).…”

“…Class V and VII chitin synthases contain a myosin motor domain (MMD) in their N-terminal region (22). Functional characterization of the seven chitin synthase genes (CHS1 to CHS7) from Magnaporthe oryzae revealed that individual CHS genes play diverse roles (21).…”

Myosin Motor-Like Domain of Class VI Chitin Synthase CsmB of <i>Aspergillus nidulans</i> Is Not Functionally Equivalent to That of Class V Chitin Synthase CsmA

“…[8][9][10][11][12][13][14] These investigations indicate that chitin synthases with MMD play important roles in hyphal tip growth and the invasion of host cells. Since the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe and the dimorphic yeast Candida albicans do not possess these orthologs in their genomes, chitin synthases with MMD are likely to play critical roles in polarized growth, especially in filamentous fungi.…”