Rosa hybrida Rh ERF 1 and Rh ERF 4 mediate ethylene‐ and auxin‐regulated petal abscission by influencing pectin degradation

The timing of plant organ abscission is modulated by the balance of two hormones, ethylene and auxin, while the mechanism of organ shedding depends on the loss of middle lamella pectin in the abscission zone ( AZ ). However, the mechanisms involved in sensing the balance of auxin and ethylene and that affect pectin degradation during abscission are not well understood. In this study, we identified two members of the APETALA 2/ethylene‐responsive factor ( AP 2/ ERF ) transcription factor family in rose ( Rosa hybrida ), Rh ERF 1 and Rh ERF 4 which play a role in petal abscission. The expression of Rh ERF 1 and Rh ERF 4 was influenced by ethylene and auxin, respectively. Reduced expression of Rh ERF 1 or Rh ERF 4 was observed to accelerate petal abscission. Global expression analysis and real‐time PCR assays revealed that Rh ERF 1 and Rh ERF 4 modulate the expression of genes encoding pectin‐metabolizing enzymes. A reduction in the abundance of pectin epitopes was detected in the AZ s of Rh ERF 1 and Rh ERF 4 ‐silenced plants by immunofluorescence microscopy analysis. In addition, Rh ERF 1 and Rh ERF 4 were shown to bind to the promoter of the pectin‐metabolizing gene β ‐ GALACTOSIDASE 1 ( Rh BGLA 1 ), and reduced expression of Rh BGLA 1 delayed petal abscission. We conclude that during petal abscission, Rh ERF 1 and Rh ERF 4 integrate and coordinate ethylene and auxin signals to modulate pectin metabolism, in part by regulating the expression of Rh BGLA 1 . This study reports a mechanism for sensing the auxin/ethylene balance associated with modulating petal abscission via degradation of pectin. We found that the expression levels of RhERF1 and RhERF4 are influenced by ethylene and auxin, respectively, and that RhERF1 and RhERF4 act together to modulate pectin degradation in the abscission zone by directly regulating the β‐galactosidase gene RhBGLA1 .