Chitin is a globally abundant
polymer widely distributed throughout eukaryotes that has been well characterized in only a few lineages. Diatoms are members of the eukaryotic lineage of stramenopiles. Of the hundreds of diatom genera, two produce long fibers of
chitin that extrude through their cell walls of
silica. We identify and describe here genes encoding putative
chitin synthases in a variety of additional diatom genera, indicating that the ability to produce
chitin is more widespread and likely plays a more central role in diatom biology than previously considered. Diatom
chitin synthases fall into four phylogenetic clades. Protein domain predictions and differential gene expression patterns provide evidence that
chitin synthases have multiple functions within a diatom cell. Thalassiosira pseudonana possesses six genes encoding three types of
chitin synthases. Transcript abundance of the gene encoding one of these
chitin synthase types increases when cells resume division after short-term
silicic acid starvation and during short-term limitation by
silicic acid or
iron, two nutrient conditions connected in the environment and known to affect the cell wall. During long-term
silicic acid starvation transcript abundance of this gene and one additional
chitin synthase gene increased at the same time a
chitin-binding
lectin localized to the girdle band region of the cell wall. Together, these results suggest that the ability to produce
chitin is more widespread in diatoms than previously thought and that a subset of the
chitin produced by diatoms is associated with the cell wall.