Modulating the strigolactone pathway to optimize tomato shoot branching for vertical farming

Optimizing plant architecture for specific cultivation methods is essential for enhancing fruit productivity. Unlike indeterminate growth plants, the total productivity of determinate growth plants relies on cumulative fruit production and synchronized fruit ripening from both main and axillary shoots. Here, we focused on SlD14 and SlMAX1, two key genes involved in the regulation of strigolactone (SL) signaling and biosynthesis, with the goal of maximizing yield and synchronizing fruit ripening by fine-tuning axillary shoot growth. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) technology, we found that the sld14, slmax1, and sld14 slmax1 mutant plants exhibited reduced plant height and increased axillary shoot proliferation compared to wild-type plants. However, these mutants showed reduced yield and delayed ripening, likely due to a source-sink imbalance caused by excessive axillary shoot development. A weak sld14 allele displayed a milder phenotype, maintaining total fruit yield and harvest index despite smaller individual fruit size. These findings indicate that allelic variation in SL-related genes can influence plant architecture and yield components. Our results suggest that weak or partial alleles may serve as promising targets for tailoring tomato architecture to space-limited cultivation systems.