Chromosome Behaviour in the Genus Trithuria (Hydatellaceae)
Research to understand the characteristics of mitotic and meiotic behaviour of chromosomes from an extant early angiosperm family with respect to their potential importance for the general course of chromosome evolution.
The phylogenetic repositioning near the base of extant angiosperms drew wide international attention to the Hydatellaceae – a semi-aquatic family consisting of one genus, Trithuria Hook.f., with twelve species occurring in Australia, New Zealand, and India. The current research programmes in the Jodrell Laboratory that have been focused on taxa with key events in the evolution of extant lineages, have significantly contributed to our collective knowledge of the early angiosperm evolution based on phenotypic, micromorphological and phylogenetic analyses of Trithuria. But, the genus Trithuria – and hence the whole family Hydatellaceae – is neither karyosystematically nor cytogenetically characterised well enough to evaluate their infrageneric cyto/genetic relationships to complement the present phylogenetic changes. Only preliminary data are available on chromosome number and genome size, and none on chromosome structure, behaviour and ploidy constitution. Synteny and genomic relationships between any of the species are virtually unknown. There are currently no cytogenetic data on inter-species hybridisation events in overlapping habitats as fundamental indicators of possible horizontal gene flow and allopatric versus sympatric speciation processes. This gap in karyological knowledge is obstructing crucial steps towards a better understanding of reproductive regulation and population dynamics.
This project, started in 2011, extends Kew’s Hydatellaceae research to the investigation of chromosome behaviour during mitosis and meiosis, and the potential influence of in vitro reproduction/cultivation in selected Trithuria genotypes. The results will evocatively amalgamate information on early forms of mitosis, meiosis, chromosomal rearrangements and phenotype variability in Trithuria polyploids. It is vital to verify the type of polyploidy, which may represent only a different cytotype of the same species rather than a different species, therefore, giving distinctive implications for the geobotanic structure and distribution of individual habitats of the genus. Thus, it becomes imperative to foster cytogenetic and karyosystematic chromosome research on Trithuria.
The current experimental work is centred on the estimation of the sporophytic chromosome numbers of different Trithuria genotypes and – if present – their aneuploid frequencies and ploidy level(s) of individual species. These data will allow us to calculate the basic chromosome number(s) of the genus. Our first extensive analyses of the process of meiosis of Trithuria submersa Hook.f. have shown significant irregularities, which seem to unwrap a plethora of diagnostic key characters. Further project steps will analyse potential inter-species cross-hybridisation and genomic rearrangement events by using GISH on orthologous chromosome segments and define subgenomic relationships. These results will considerably supplement the known phylogenetic and phenotypic data by defining mutual chromosomal relationships and open a new avenue into using 3D-microscopy by national co-operation. The project will disseminate new knowledge on ploidy status and possible chromosome arrangements on a family level. The virtual genome dissection can hallmark speciation events allowing chromosome segments to become excellent tools for genetics and genomics in extant early angiosperms. Because of the research layout, the project will not only strengthen the collaboration among Genetics, Micromorphology and Conservation Biotechnology sections in the Jodrell Laboratory, it will also integrate external expertise of 3D-analysis of Birkbeck University of London into Kew’s current evo/devo research programme.
Project partners and collaborators
Maud Dumoux, Gita Panchal (Birkbeck, University of London)