Chitosan Is Necessary for the Structure of the Cell Wall, and Full Virulence of .

Smut fungi comprise a large group of biotrophic phytopathogens infecting important crops, such as wheat and corn. is a plant pathogenic fungus responsible for common smut in maize and teocintle. Through our analysis of the transcriptome of the yeast-to-mycelium dimorphic transition at acid pH, we determined the number of genes encoding chitin deacetylases of the fungus, and observed that the gene encoding one of them (UMAG_11922; ) was the only one up-regulated. The mutation of this gene and the analysis of the mutants revealed that they contained reduced amounts of chitosan, were severely affected in their virulence, and showed aberrant mycelial morphology when grown at acid pH. When the gene was reinserted into the mutants by the use of an autonomous replication plasmid, virulence and chitosan levels were recovered in the retro mutant strains, indicating that the gene was involved in these features. These data revealed that chitosan plays a crucial role in the structure and morphogenesis of the cell wall during mycelial development of the fungus, and that in its absence, the cell wall becomes altered and is unable to support the stress imposed by the defense mechanism mounted on by the plant host during the infection process.