Candida albicans has four chitin synthases from three different enzyme classes which deposit chitin in the cell wall, including at the polarized tips of growing buds and hyphae, and sites of septation. The two class I enzymes, Chs2 and Chs8, are responsible for most of the measurable chitin synthase activity in vitro, but their precise biological functions in vivo remain obscure. In this work, detailed phenotypic analyses of a chs2Δchs8Δ mutant have shown that C. albicans class I chitin synthases promote cell integrity during early polarized growth in yeast and hyphal cells. This was supported by live cell imaging of YFP-tagged versions of the class I chitin synthases which revealed that Chs2-YFP was localized at sites of polarized growth. Furthermore, a unique and dynamic pattern of localization of the class I enzymes at septa of yeast and hyphae was revealed. Phosphorylation of Chs2 on the serine at position 222 was shown to regulate the amount of Chs2 that is localized to sites of polarized growth and septation. Independently from this post-translational modification, specific cell wall stresses were also shown to regulate the amount of Chs2 that localizes to specific sites in cells, and this was linked to the ability of the class I enzymes to reinforce cell wall integrity during early polarized growth in the presence of these stresses.
Bibliographical noteOpen Access funded by Medical Research Council
We thank Kevin Mackenzie in the Microscopy and Histology Core Facility (Institute of Medical Sciences, University of Aberdeen), and Donna MacCallum for helpful statistical advice. This work was supported by grants from the Wellcome Trust (0868827 and 080088) including a Wellcome Trust Strategic Award (097377) and an Investigator Award to NG (101873), an MRC New Investigator Award to ML (MR/J008230/1) and a PhD scholarship awarded to KP from the Ministry of Sciences and Technology and Chiang Mai University, Thailand. Author contributions are as follows: KP constructed strains, performed the majority of the experiments, analyzed the data and contributed to the preparation of the manuscript. JA produced Fig. S1 using the data from the phosphoproteomic analysis conducted by SP and AB. NG conceived and designed experiments, analyzed data and commented on drafts of the manuscript. ML constructed strains, conceived, designed and performed experiments, analyzed data and wrote the manuscript.
- candida albicans
- cell wall
- chitin synthase
- class I chitin synthase
- polarized growth