Genome Editing of a Carotenogenic Gene for Lycopene Enhancement Increases Heavy Metal Stress Susceptibility in Tomato ( Solanum lycopersicum L. )

Improving the nutritional quality and abiotic stress tolerance of crop plants is essential for sustainable agriculture and global food security. Recent advances in genome editing, particularly the CRISPR/Cas9 system, have enabled precise modification of metabolic pathways to enhance valuable traits such as carotenoid accumulation. The present study aimed to enhance fruit lycopene content and assess associated stress responses in tomato (Solanum lycopersicum L.) through targeted genome editing of the lycopene beta cyclase (β-LCY, EC 5.5.1.19) gene, encoding for a key enzyme in the carotenoid biosynthetic pathway. A Csy4-based multiplex CRISPR/Cas9 approach was applied to edit β-LCY in three tomato genotypes, including two cultivated varieties and the wild species S. peruvianum L. Genotypic analysis revealed significant genotype-dependent differences in editing efficiency. The β-LCY knockout lines exhibited markedly increased lycopene accumulation in fruits, resulting in enhanced pigmentation. However, when subjected to cadmium stress, these lines showed greater susceptibility than wild-type plants, with pronounced wilting and stress symptoms. Physiological, biochemical, and metabolomic analyses confirmed disruption of stress-response mechanisms associated with carotenoid pathway modification. These findings demonstrate that while genome editing can successfully enhance desirable metabolic traits, it may also impair abiotic stress tolerance. This study provides new insight into the complex interplay between the carotenoid biosynthetic pathway and stress adaptation in tomato.