Differential expression of chitin synthase genes during temperature-induced dimorphic transitions in Paracoccidioides brasiliensis

Fragments of five genes encoding chitin synthase enzymes were identified in the dimorphic fungus Paracoccidioides brasiliensis by polymerase chain reaction (PCR) amplification of conserved CHS gene domains. These represent several classes of enzyme: PbrCHS1, class I; PbrCHS2, class II; PbrCHS3, class IV; and PbrCHS4 and PbrCHS5, class V. Expression of these genes during the temperature regulated dimorphic transition from yeast to mycelium and from mycelium to yeast was determined by Northern analysis. One gene (PbrCHS3) was not expressed at detectable levels. The others were regulated by morphology and/or by the growth phase of the organism. Despite the fact that yeast cells contain more chitin than hyphal cells, the levels of mRNA for PbrCHS1, PbrCHS2, PbrCHS4 and PbrCHS5 were higher in hyphal cells than in yeast cells. This supports observations in other fungi that transcript levels often do not correlate with chitin content and that post-transcriptional regulation of CHS gene expression is important for morphogenesis.