Lead


Lay summary
This project focussed on fundamentals of sexual reproduction in representatives of lichen-forming ascomycetes, an extremely poorly investigated aspect in this large group of nutritional specialists, which comprises approx. 20% of all fungi. Mating systems in diverse families and mating type genes in Teloschistaceae were of central interest. A high percentage of lichen-forming ascomycetes are very rarely fertile, but disperse efficiently by means of vegetative symbiotic propagules. The question whether such taxa are cross- or self-fertilizers (hetero- or homothallic) was studied with fingerprinting techniques applied to single spore isolates derived from the same ascus, i.e. the progeny of meiosis. More than 20 rarely fertile species from four families of Lecanoromycetes were included in this analysis; rare, endangered as well as very common and widespread species being studied. All of these rarely and irregularly fertile species turned out to be cross-fertilized, i.e. recombine. These findings are useful for designing conservation strategies for endangered species. Mating systems were also studied in a wide range of Xanthoria secies (Teloschistaceae). Cross-fertilised species are easily identified with fingerprinting techniques, but self-fertile ones are more difficult to characterize; only a detailed analysis of the mating type locus allows a proper interpretation. Fungal MAT loci evolve very rapidly; therefore they are very difficult to investigate. Ascomycetes typically have a one locus, two allele mating system, both alleles (MAT 1-1, or MAT 1-2, respectively) being completely different from each other; therefore they are referred to as idiomorphs. Only one MAT allele, but not the corresponding idiomorph of a heterothallic lichen-forming ascomycete had been known to science when Sandra Scherrer started to characterize the first complete mating type loci with flanking regions in lichen-forming ascomycetes of the genus Xanthoria: MAT1-1, encoding an alpha domain protein, and MAT 1-2, encoding a HMG box protein, were identified in five heterothallic and two homothallic Xanthoria species. Both homothallic species were already assumed to be self-fertilizers on the basis of our fingerprinting assays. Based on these studies the genetics of self-fertile species are better understood. The MAT locus of all siblings of meiosis of the homothallic X. elegans was shown to contain MAT 1-1 and MAT 1-2 in opposite orientation, whereas all siblings of X. parietina contain MAT 1-2, MAT 1-1 having been lost. Heterothallic species have MAT 1-1 or MAT 1-2, respectively, in half of the progeny of meiosis.Robust multilocus phylogenies form the backbone of our investigations on the role of changes from hetro-to homothallism during speciation processes. In his PhD thesis Christof Eichenberger investigated 36 teloschistaceaen species, the focus being on the genera Xanthoria and Xanthomendoza. 493 complete sequences were achieved, all deposited in GenBank database (publications in preparation). For PDF-files of publications please see under http://botserv1.uzh.ch/home/honegger/index.html