Strain, procedures, and tools for reproducible genetic transformation and genome editing of Spirodela polyrhiza (L.) Schleid.

Duckweeds (Lemnaceae) have excellent potential as plant systems for fundamental and applied research due to the ease of cultivation, their 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 insertional mutagenesis, reporter gene expression, gene editing, and other methods to modify gene expression. Here, we present a robust transformation protocol for a publicly available strain of Spirodela polyrhiza, SP162, that we identified to be amenable to Agrobacterium-mediated stable transformation via tissue culture. The transformation procedure allows stable expression of different reporter genes and selectable markers and enables CRISPR/Cas9-mediated genome editing. Due to the lack of a small RNA-based silencing response, S. polyrhiza SP162 also sustains prolonged periods of transgene activity in Agrobacterium-mediated transient expression assays. Thus, SP162 is an ideal reference strain for developing improved transformation procedures and applications in S. polyrhiza. To promote duckweed research and encourage the adoption of S. polyrhiza in research laboratories, we have made SP162 (ID#: 5676) and its genome publicly available and provide here detailed procedures for its cultivation and transformation.