Dr Alex Ware - University of Nottingham

Dr Alex Ware

Roots to shoots: relocation of nutrient uptake in duckweeds at cellular resolution

Duckweeds are the world's smallest and fastest-growing flowering plants. They are aquatic and free-floating, reproduce clonally, and have a drastically simple body plan for a flowering plant, with the entire shoot system fused into a single flattened ‘frond’. They also exhibit a trajectory of root loss: in early-diverging genera the root is vestigial, and in more derived genera it is absent entirely. I have previously shown that the duckweed root is no longer needed for its ancestral function of nutrient uptake, instead taking up nutrients directly into the frond. This frond, despite its apparent simplicity, retains a full angiosperm body plan, and is a compressed fusion of stem and leaf. Duckweeds are therefore performing nutrient uptake in an organ homologous to a leaf, which is unusual among angiosperms, and the cellular mechanisms underlying this transfer of function are not understood.
To address this, I have generated single-nucleus transcriptomic atlases of shoots and roots from Spirodela polyrhiza, Lemna minor and Wolffia australiana, alongside the aroid Pistia stratiotes, which independently colonised the free-floating aquatic niche. Integration of these datasets across species has revealed a cell population conserved across all duckweed shoots, which expresses a broad suite of nutrient-uptake genes canonically restricted to the root in terrestrial species. In Lemna, optimisation of whole-mount hybridisation chain reaction FISH has localised this cell type to the underside of the frond. I am now working to establish what specifies its identity, how it evolved, and whether the machinery underlying cellular functional relocation is portable.