Visualizing cassava bacterial blight at the molecular level using CRISPR-mediated homology-directed repair

Research on a few model, plant-pathogen systems has benefitted from years of tool and resource development. This is not the case for the vast majority of economically and nutritionally important plants, creating a crop improvement bottleneck. Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam), is an important disease in all regions where cassava (Manihot esculenta Crantz) is grown. Here we describe development of a tool for molecular-level visualization of CBB dynamics in vivo. Using CRISPR-mediated homology-directed repair (HDR), we generated plants containing scarless insertion of a GFP reporter at the CBB susceptibility (S) gene MeSWEET10a. Activation of MeSWEET10a-GFP by Xam was subsequently visualized at transcriptional and translational levels. Development of this tool was facilitated by a time-saving, adaptable strategy for identifying successful products of HDR, currently a limiting factor in plant research. This strategy has the potential to enable such research in other systems, improving the practicality of HDR-based experimentation.