Red fruit, orange fruit, orange fruit, red fruit: Genome editing in tomato

Red fruit, orange fruit, orange fruit, red fruit: Genome editing in tomato

Efficient in planta gene targeting in tomato using geminiviral replicons and the CRISPR/Cas9 system

Dahan-Meir T, Filler-Hayut S, Melamed- Bessudo C, Bocobza S, Czosnek H, Aharoni A,

Levy AA (2018) The Plant Journal 95, 5-16. https://onlinelibrary.wiley.com/doi/full/10.1111/tpj.13932

Gene editing has revolutionised biology. Researchers can now swap promoters to change the expression levels of genes, test modified genes in their original genomic context, and test various transgenes in a fixed location, thereby minimising position effects. But the frequencies of gene replacement events were low (~1%), until Dahan-Meir et al. reported remarkable frequencies for both targeted gene mutagenesis and gene replacement in tomato. For targeted gene mutagenesis they used CRTISO, which encodes carotenoid isomerase, and PSY1, which encodes a phytoene synthase. They chose these genes because the phenotypes are obvious – tangerine mutants (defective in CRTISO) have orange fruits and psy1 mutants have yellow fruits. The frequencies of mutagenesis were remarkably high, from 50-70% for PSY1 and 90% for CRTISO. For gene targeting they used a deletion mutant in CRTISO: 25% of the primary transformants had repaired the tangerine mutation and had red fruit. Getting gene targeting to work routinely at such efficiencies will undoubtedly require optimizing the system for various plant species, loci and cell types, but in tomato it is now feasible.

Sheila McCormick, Research Highlights Editor