| In Arabidopsis flowers, an ADP-ribosylation factor GTPase activating protein, NEVERSHED (NEV), is required for organ abscission. Mutations in NEV severely disrupt the organization of the Golgi apparatus and cause vesicle hyperaccumulation in abscission zone cells at the time of shedding. To identify factors that may physically interact with or act downstream of NEV, a screen was conducted for mutants that rescue organ shedding in nev flowers. Four dominant suppressor mutants were found to contain mutations predicted to affect the extracellular domain of the leucine-rich repeat receptor-like kinase SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 (SERK1). Since the previously characterized serk1-1 allele, known to eliminate kinase activity, also dominantly restores organ abscission in nev flowers, we conclude that reduced levels of SERK1 are sufficient to allow abscission in this context.;To determine whether loss of SERK1 activity might affect the subcellular defects observed in nev flowers, transmission electron microscopy of nev serk1 flowers was carried out. Loss of SERK1 was discovered to restore Golgi structure in nev flowers, indicating that disruption of this organelle is likely responsible for preventing abscission. We have also found that the abscission zones of nev serk1 double mutant flowers are enlarged, and show significantly increased cell numbers and cell expansion compared to wild type. This phenotype is reminiscent of that seen in plants constitutively expressing the putative ligand, INFLORESCENCE DEFICIENT in ABSCISSION (IDA), a positive regulator of floral organ abscission. Thus, it is possible that higher levels of IDA or its activated receptor(s) may be present in nev serk1 abscission zone cells. Our results suggest the possibility that NEV may promote abscission by regulating the trafficking of receptor-like kinases such as SERK1. |
