Professor Avraham Levy
ved Plant Sciences Department, The Weizmann Institute of Sciences, Rehovot, Israel, forelese over følgende emne:
Genetic and epigenetic mechanisms of gene expression rewiring in hybrids and polyploids
Foreleseren:
Professor Levy er professor i genetikk og arbeider med artsdannelse, spesielt i forbindelse med hybridisering og kromosomfordobling. Han arbeider først og fremst med planter, men også med andre organismer slik som gjærsopp (se f.eks. Science 324: 659-662, 2009).
Abstract:
Genome merging, in interspecific hybrids and allopolyploids, is associated with novel patterns of gene expression. We have analyzed the genetic and epigenetic basis for this rewiring in two model systems, namely a yeast hybrid and a synthetic wheat hybrid and allopolyploid. In yeast, we have analyzed how hybrid-specific gene expression patterns are generated from the divergence in regulatory components between the parental species. We have distinguished changes in regulatory sequences of the gene itself (cis) from changes in upstream factors (trans). Expression divergence was mostly due to changes in cis. Changes in trans were condition-specific and reflected mostly differences in environmental sensing. In the hybrid, over-dominance in gene expression occurred through novel cis-trans interactions or, more often, through modified trans regulation associated with environmental sensing. We will discuss the phenotypic impact of hybrid-specific expression patterns. In wheat we have previously shown rapid genetic and epigenetic alterations in genes or transposons at the onset of hybridization and/or in nascent allopolyploids. As small RNAs are candidates for affecting these events, we have analyzed the changes in small RNAs (Micro and siRNAs) populations in hybrids and allopolyploids and their connection with genes and transposon expression. We show that small RNA populations are altered in hybrids and polyploids with the strongest changes observed just after polyploidization. Overall, in the first generation of the polyploid, there was a massive suppression of siRNAs that corresponds to repeats and transposons. This is consistent with the observed transcriptional activation of transposons upon polyploidization and supports the role of siRNAs in heterochromatinization and repression of transposons. These works emphasize how different levels of regulation, namely genetic, epigenetic and environmental, can bring about hybrid-specific expression patterns in lower and higher eukaryotes.