The RhLOL1–RhILR3 module mediates cytokinin-induced petal abscission in rose

Summary In many plant species, petal abscission can be considered the final step of petal senescence. Cytokinins (CKs) are powerful suppressors of petal senescence; however, their role in petal abscission is ambiguous. Here, we observed that, in rose ( Rosa hybrida ), biologically active CK is accumulated during petal abscission and acts as an accelerator of the abscission process. Using a combination of reverse genetics, and molecular and biochemical techniques, we explored the roles of a LESION SIMULATING DISEASE1 (LSD1) family member Rh LOL1 interacting with a bHLH transcription factor Rh ILR3 in CK-induced petal abscission. Silencing Rh LOL1 delays rose petal abscission, while the overexpression of its ortholog Sl LOL1 in tomato ( Solanum lycopersicum ) promotes pedicel abscission, indicating the conserved function of LOL1 in activating plant floral organ abscission. In addition, we identify a bHLH transcription factor, Rh ILR3, that interacts with Rh LOL1. We show that Rh ILR3 binds to the promoters of the auxin signaling repressor auxin/indole-3-acetic acid ( Aux/IAA ) genes to inhibit their expression; however, the interaction of Rh LOL1 with Rh ILR3 activates the expression of the Aux/IAA genes including Rh IAA4-1 . Silencing Rh IAA4-1 delays rose petal abscission. Our results thus reveal a Rh LOL1– Rh ILR3 regulatory module involved in CK-induced petal abscission via the regulation of the expression of the Aux/IAA genes.