CRISPR/Cas9-mediated SlAN2 mutants reveal various regulatory models of anthocyanin biosynthesis in tomato plant.

Key Message: Combining phenotype and gene expression analysis of the CRISPR/Cas9-induced SlAN2 mutants, we revealed that SlAN2 specifically regulated anthocyanin accumulation in vegetative tissues in purple tomato cultivar 'Indigo Rose.' Anthocyanins play an important role in plant development and also exhibit human health benefits. The tomato genome contains four highly homologous anthocyanin-related R2R3-MYB transcription factors: SlAN2, SlANT1, SlANT1-like, and SlAN2-like/Aft. SlAN2-like/Aft regulates anthocyanin accumulation in the fruit; however, the genetic function of the other three factors remains unclear. To better understand the function of R2R3-MYB transcription factors, we conducted targeted mutagenesis of SlAN2 in the purple tomato cultivar 'Indigo Rose' using clustered regularly interspersed short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9). The SlAN2 mutants had a fruit color and anthocyanin content similar to cv. 'Indigo Rose,' while the anthocyanin content and the relative expression levels of several anthocyanin-related genes in vegetative tissues were significantly lower in the SlAN2 mutant relative to cv. Indigo Rose. Furthermore, we found that anthocyanin biosynthesis is controlled by different regulators between tomato hypocotyls and cotyledons. In addition, SlAN2 mutants were shorter, with smaller and lighter fruits than cv. 'Indigo Rose.' Our findings further our understanding of anthocyanin production in tomato and other plant species.