Strain, procedures, and tools for reproducible genetic transformation and genome editing of the emerging plant model <i>Spirodela polyrhiza</i>

Duckweeds (Lemnaceae) have excellent potential for fundamental and applied research due to ease of cultivation, small size, and continuous fast clonal growth. However, their usage as model organisms and platforms for biotechnological applications is often limited by the lack of universal genetic manipulation methods necessary for transgene expression, gene editing, and other methods to modify gene expression. To identify suitable strains for genetic manipulation of the giant duckweed, Spirodela polyrhiza, we screened several genotypes for callus induction and regeneration and established genetic transformation. We identified SP162 to be amenable to Agrobacterium-mediated transformation via tissue culture. The procedure is robust and reproducible across laboratories, allowing stable expression of different reporter genes and selectable markers, enabling CRISPR/Cas9-mediated genome editing. In addition, due to a weak small RNA-based silencing response, S. polyrhiza sustains prolonged periods of transgene activity in transient expression assays. To promote duckweed research and encourage the adoption of S. polyrhiza, we have made SP162 (ID#: 5676) and its genome publicly available and provide here detailed procedures for its cultivation and transformation. Furthermore, we created a web server to explore its genome, retrieve gene sequences, and implement orthologous gene search and a gRNA design function for diverse CRISPR/Cas-based applications (https://agxu.uni-mainz.de/SP162/).