Elucidation of phylogeny and genome diversity within the duckweed genus Wolffia, based on sequence and karyotype variability

• Applicants: Professor Dr. Ingo Schubert; Dr. Anton Stepanenko, Ph.D.
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575044183

Duckweeds are a small, cosmopolitan and organ-reduced aquatic monocot family, floating on freshwater, propagating asexually in most cases, and characterized by an extremely fast biomass doubling. Therefore, and because of their optimal composition of carbohydrates and proteins and easy-to-harvest biomass, they are of commercial interest for generation of feed, food and biofuel, as well as of recombinant proteins and for wastewater remediation. Of the 5 genera: Spirodela, Landoltia, Lemna, Wolffia and Wolffiella, comprising together hitherto 35 species, the species of the latter three are hardly to discriminate by morphological features. Even barcoding with plastid markers yields in some cases no reliable results. Moreover, chromosome number and genome size are reported to vary considerably between clonal accessions assigned to distinct species. These features, together with their rapid vegetative propagation, their peculiar life style and hibernating structures (turions), make them interesting subjects for evolutionary, developmental and genomic studies. The clonal accessions of genus Wolffia with 11 putative species of small, round, rootless, green bodies (the fronds) are morphologically very similar and apparently display a high intraspecific variability of genome size, chromosome number, presumably representing ploidy variants and interspecific hybrids, similar as observed for accessions belonging to the genus Lemna. Therefore, this proposal is focused on the genus Wolffia and aimed to elucidate the phylogenetic relationship and taxonomy of ~120 accessions assigned to the 11 putative species of the genus. This should be done by applying several independent approaches to arrive at safe conclusions. The approaches will include genome size measurement, chromosome counting, next generation sequencing, comparing plastid and nuclear gene sequences (e.g. tubulin gene introns, collaboration with Laura Morello’s group of IBBA, Milan, Italy, and 5S/35S rDNA sequences), genotyping-by-sequencing, as well as genomic in situ hybridization (GISH). We expect that this combination of methods will uncover the species affiliation of the tested accessions and reveal potential ploidy variants and interspecific hybrids, including the proportion of ancestral genomes and their maternal or paternal origin. The results will shed new light on the infrageneric structure of genus Wolffia and potentially open avenues for breeding efforts and for studies of evolutionary consequences of reticulate evolution in this genus. Well characterized accessions will be provided for cryopreservation as references for distinct species.

• DFG Programme: Research Grants