Cyto-Nuclear Interactions in Tragopogon (Asteraceae) Allopolyploids: Insight from rbcL and rbcS

Gene products from organellar genomes (chloroplast and mitochondria) can interact with nuclear gene products in a variety of pathways. Most protein complexes consisting of multiple subunits have proteins encoded by both nuclear and organellar genomes. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) is involved in carbon dioxide fixation in the Calvin cycle and has two subunits: a large subunit (rbcL) encoded by the chloroplast genome and a small subunit (rbcS) that is encoded by the nuclear genome. How these subunits interact in hybrids and allopolyploids is unknown.  In order to explore the inheritance and expression of both maternal and paternal homeologs of the nuclear-encoded rbcS, and to determine which of the nuclear homeologs of rbcS is interacting with the chloroplast-encoded subunit rbcL, rbcS was amplified from three diploid species of Tragopogon (T. dubius, T. pratensis and T. porrifoilius), which are the parents of the allopolyploids T. mirus and T. miscellus. Sequence analysis of rbcS from the diploid parents showed the presence of seven single nucleotide polymorphisms (SNPs). Based on this variation among the parents, progenitor-specific markers are being designed, which will be used to amplify rbcS homeologs from reciprocally generated synthetic polyploid lines of T. mirus and T. miscellus. We expect that both parental copies of rbcS will be present in the genomes of the synthetic polyploids, but that the maternal homeolog of rbcS will be expressed and will interact with rbcL from that same progenitor.