Editing of SlMYB60 Reveals a Role in Cuticle Formation in Tomato

Under climate change, yield stability depends heavily on the ability to develop resilient crops, better adapted to water scarcity. Studies in model systems have uncovered molecular pathways and genes that potentiate the plant response to environmental stress. CRISPR-based editing technologies enable the precise and rapid transfer of beneficial traits from model species to crops. Previous work identified Solanum lycopersicon MYB60 (SlMYB60) as the functional ortholog of the Arabidopsis guard cell-related AtMYB60 transcription factor. Loss of AtMYB60 function results in reduced stomatal opening and enhanced stress resistance, providing a valuable target for crop improvement. Here, we report the CRISPR-mediated exploitation of SlMYB60 in two tomato commercial varieties. Unexpectedly, editing of SlMYB60 did not result in reduced stomatal opening and enhanced stress resistance. Independent edited lines showed increased stomatal size, enhanced leaf water loss, and cuticle permeability. RNAseq analyses revealed that the expression of genes involved in cell wall and cuticle metabolism was altered in the edited lines. Scanning electron microscope analysis of leaf epidermis revealed defects in cuticle deposition and in the formation of outer cuticle ledges. As opposed to the guard cell-specific activity of the AtMYB60 promoter, we found that the SlMYB60 promoter was active in both stomata and epidermal cells. Our findings indicate functional divergence between AtMYB60 and SlMYB60, providing valuable insights into species-specific regulatory mechanisms and emphasizing the complexities of translating gene-editing strategies across plant systems.