Transcription factors SlBBX20 and SlMYB9 in tomato modulate plant height through gibberellin metabolic and response pathways.

Gibberellins (GAs) are plant hormones that regulate growth and development. We investigated how a transcription factor, SlBBX20, modulates plant height by affecting GA metabolism and response in tomato (Solanum lycopersicum L.). We found that overexpression of SlBBX20 caused dwarfism, which was rescued by GA treatment, while knockout of SlBBX20 increased plant height. SlBBX20 directly activated the expression of GA metabolic oxidase genes (SlGA2ox1, SlGA2ox4, and SlGA2ox5) and repressed the expression of a GA-responsive gene, SlMYB9. Plants overexpressing SlMYB9 grew taller than wild type and knockout plants after GA treatment, as SlMYB9 inhibited the expression of SlGA2ox4 and SlGA2ox5. Restoring SlMYB9 expression in SlBBX20-overexpressing plants reversed the dwarf phenotype. Our study reveals a novel regulatory module involving SlBBX20-SlMYB9-SlGA2 oxidase for controlling plant height and provides insights into the molecular mechanisms of GA action in plants.