Abstract
Leaf senescence is a highly-programmed developmental process during the plant life cycle. ABA plays an important role in leaf senescence. However, the mechanism underlying ABA-mediated leaf senescence, particularly the upstream epigenetic regulatory network, remains largely unclear. Here, we identified that SlJMJ4, a Jumonji C (jmjC) domain-containing protein in tomato, specifically demethylates di- and tri-methylations of lysine 27 of histone H3 (H3K27) in vitro and in vivo. Overexpression of SlJMJ4 results in premature senescence phenotype and promotes dark- and ABA-induced leaf senescence in tomato. Under dark condition, SlJMJ4-promoted leaf senescence is associated with upregulated expression of transcription factors (SlORE1 and SlNAP2) and senescence-associated genes (SlSAG113, SlSAG12) via removal of H3K27me3. In responses to ABA, overexpression of SlJMJ4 increases its binding at the loci of SlORE1, SlNAP2, SlSAG113, SlSAG12, SlABI5 and SlNCED3 and decreases their H3K27me3 levels, and therefore activates their expression and mediates ABA-induced leaf senescence in tomato. Taken together, these results demonstrate that SlJMJ4 plays a positive role in leaf senescence in tomato and is implicated in ABA-induced leaf senescence by binding to many key genes related to ABA synthesis and signaling, transcription regulation and senescence and hence promoting their H3K27me3 demethylation.