Chitinases Are Essential for Cell Separation in Ustilago maydis

Abstract

Chitin is an essential component of the fungal cell wall, providing rigidity and stability. Its degradation is mediated by chitinases and supposedly ensures the dynamic plasticity of the cell wall during growth and morphogenesis. Hence, chitinases should be particularly important for fungi with dramatic morphological changes, such as Ustilago maydis. This smut fungus switches from yeast to filamentous growth for plant infection, proliferates as a mycelium in planta, and forms teliospores for spreading. Here, we investigate the contribution of its four chitinolytic enzymes to the different morphological changes during the complete life cycle in a comprehensive study of deletion strains combined with biochemical and cell biological approaches. Interestingly, two chitinases act redundantly in cell separation during yeast growth. They mediate the degradation of remnant chitin in the fragmentation zone between mother and daughter cell. In contrast, even the complete lack of chitinolytic activity does not affect formation of the infectious filament, infection, biotrophic growth, or teliospore germination. Thus, unexpectedly we can exclude a major role for chitinolytic enzymes in morphogenesis or pathogenicity of U. maydis. Nevertheless, redundant activity of even two chitinases is essential for cell separation during saprophytic growth, possibly to improve nutrient access or spreading of yeast cells by wind or rain.

Endosomal assembly and transport of heteromeric septin complexes promote septin cytoskeleton formation

“…; n=4 independent experiments, at least 50 hyphae were counted per strain and experiment; note that septum formation is given relative to the values of unipolar or bipolar hyphae set at 100%). (C) Relative chitinase activity of septin deletion strains as assessed by detecting endochitinase Cts1 (Koepke et al, 2011;Langner et al, 2015) in the yeast (top) or hyphal form (bottom; 8 h.p.i.). Error bars represent mean±s.e.m.…”

“…Determination of Cts1 activitiy in the supernatant of cells was performed in a similar manner to in previous studies (Koepke et al, 2011;Langner et al, 2015). Note that U. maydis cells were grown at 20°C in order to prevent morphological defects.…”

Mechanisms of cytokinesis in basidiomycetous yeasts

“…Two of the enzymes Cts1 and Cts2 were required for cell separation (Langner, Ozturk et al 2015). Interestingly, the growth rates of the cts1/cts2 double mutant and the wild type were comparable suggesting no inhibition of the cell cycle due to inhibited cell separation (Langner, Ozturk et al 2015).…”

“…Two of the enzymes Cts1 and Cts2 were required for cell separation (Langner, Ozturk et al 2015). Interestingly, the growth rates of the cts1/cts2 double mutant and the wild type were comparable suggesting no inhibition of the cell cycle due to inhibited cell separation (Langner, Ozturk et al 2015). Cts1 is distributed asymmetrically within the fragmentation zone at the time when only the mother-derived primary septum is present, which suggests that it is delivered specifically from the daughter cell (Langner, Ozturk et al 2015).…”

Regulation of haplid phenotypes in Ustilago maydis by ammonium transporters and components of the b mating locus.

“…Chitin deacetylase in particular, which converts chitin to chitosan in the fungal cell wall, is vital for cell wall integrity and budding growth in other Basidiomycetes, like Cryptococcus neoformans (Baker, Specht, Donlin, & Lodge, 2007). While chitinase activity was not found to be necessary to dikaryon development, it was found to be necessary during saphrophytic growth and separation of nascent daughter cells (Langner et al, 2015), leading us to hypothesize it may play a role in haploid colony phenotype. Moreover, cell wall modification genes have been found to be dependent on products of the b mating locus for expression (Heimel et al, 2010).…”