Differential expression of chitin synthase III and IV mRNAs in ascomata of Tuber borchii Vittad

A full-length genomic clone encoding a class III chitin synthase(CHS) and one DNA fragment corresponding to a classIV CHS were isolated from the mycorrhizal fungusTuber borchii and used for an extensive expressionanalysis, together with a previously identified DNAfragment corresponding to a class II CHS. All threeChs mRNAs are constitutively expressed in vegetativemycelia, regardless of the age, mode of growth, andproliferation capacity of the hyphae. A strikingly differentsituation was observed in ascomata, where classIII and IV, but not class II, mRNAs are differentiallyexpressed in a maturation stage-dependent mannerand accumulate, respectively, in sporogenic and vegetativehyphae. These data, the first on the expressionof distinct Chs mRNAs during fruitbody development,point to the different cellular roles that can be playedby distinct chitin synthases in the differentiation ofspores of sexual origin (CHS III) or in ascoma enlargementpromoted by the growth of vegetative hyphae(CHS IV).