Functional differentiation of chitin synthases in Yarrowia lipolytica

In this study, we identified seven chitin synthase-encoding genes in the genome of the dimorphic yeast Yarrowia lipolytica. Three encoded chitin synthases with myosin motor-like domains at their N-termini, and we designated these CSM1 to CSM3, whereas four were identified as CHS1 to CHS4. To investigate the functions of these seven genes, we constructed and characterized their deletion mutants. The chs2Δ mutant formed chained cells in which daughter cells were connected with mother cells and had abnormally thick septa at the bud neck. The chs4Δ mutant showed remarkably reduced chitin content in its cell wall. The chs2Δ, csm1Δ, and csm2Δ mutants were found to be highly sensitive to chitin binding dyes, calcofluor white (CFW) and Congo red, whereas the chs4Δ mutant was resistant to CFW. These results suggest that Chs2 and Chs4 play major roles in septum formation and cell wall chitin synthesis respectively, whereas Csm1 and Csm2 are involved in the maintenance of cell wall architecture and/or cell wall integrity. The populations of filamentous cells, a type of cell population that are defined by the lengths of the cellular long and short axes, decreased in the chs3Δ mutant, suggesting that Chs3 is involved in cellular morphogenesis.