Evolution of cytonuclear coordination in Tragopogon (Asteraceae) allopolyploids : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Manawatu, New Zealand. EMBARGOED to 10 October 2024.

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Cytonuclear coordination is an important aspect in plant evolution which involves the synchronized interactions between nuclear and organellar genomes. Allopolyploidy, resulting from interspecific hybridization and genome duplication, could result in cytonuclear incompatibilities. Therefore, to coordinate cytonuclear interactions, allopolyploids may undergo alterations in duplicated nuclear gene expression via incorporating maternally biased expression patterns. To investigate cytonuclear responses to allopolyploidy, in this study, expression patterns of duplicated nuclear genes and their organelle counterparts, implicated in cytonuclear enzyme complexes, as well as dual-targeted genes were investigated in the reciprocally formed young T. miscellus allopolyploids (90-100 years) and diploid parent species; T. dubius and T. pratensis. In addition, the effect of polyploidy on morphological traits of T. miscellus allopolyploids were examined and assessed relative to parent species. The expression data showed that T. miscellus allopolyploids are regulating expression at the homeolog level, primarily through T. pratensis bias, while maintaining the total gene expression levels as to parental levels. The morphological evaluation of allopolyploids and diploids demonstrated that both reciprocal forms of T. miscellus have significantly longer, but fewer leaves compared to the diploid parent species. These findings reflect that young T. miscellus allopolyploids are certainly undergoing homeolog expression regulation to accommodate cytonuclear interactions as well as displaying morphological responses to allopolyploidy. This study provides insights into polyploid genome evolution and contributes to further understanding of the cytonuclear coordination in allopolyploids.
Compositae, Genetics, Evolutionary genetics, Plant genomes, Tragopogon