The tomato methyl-CpG-binding domain SlMBD5 promotes seed germination by repressing the gibberellin catabolism gene SlGA2ox4

Seed germination is a crucial transition in spermatophytes, regulated by gibberellins (GAs). GA levels are controlled by GA2-oxidases (GA2ox), but how DNA methylation participates in this regulation remains unclear. Here, we identified the tomato methyl-CpG-binding domain (MBD) protein SlMBD5 as a regulator of seed germination. The slmbd5 mutant exhibits delayed germination and reduced GA4/GA7 levels, which can be rescued by exogenous GA4+7 application. Transcriptomic and biochemical analyses revealed that SlMBD5 represses the GA catabolism gene SlGA2ox4 by directly binding to its hypermethylated promoter. Furthermore, we show that SlMBD5 interacts with the histone methylation reader SlEBS, forming a functional complex that promotes the transcriptional repression of SlGA2ox4. Consistent with the model that SIMBD5 promotes seed germination through its repression of SlGA2ox4, the slmbd5/slga2ox4 double mutant shows partially restored germination. This study thus reveals an SlMBD5-SlEBS module that regulates GA homeostasis to modulate seed germination in tomato.