Essential Role Of Arabidopsis Cullin1 In Jasmonate Signal Transduction

The SKPl-Cullin/Cdc53-F-box protein ubiquitin ligases (SCF) target many important regulatory proteins for degradation and play vital roles in diverse cellular processes. In the Arabidopsis genome there are 11 Cullin members (AtCUL), AtCULl was recently demonstrated to be assembled into SCF complexes containing COI1 that is a F-box protein required for response to jasmonates (JA) that regulate plant fertility and defense responses. It has been proposed that jasmonate signal would activate SCFCOI1-mediated ubiquitination and subsequent degradation of repressors of jasmonate response. Here, we present genetic and physiological data to directly demonstrate that AtCULl is necessary for normal jasmonate responses. The homozygous AtCULl mutants axr6, the heterozygous mutants axr6/AXR6, and the transgenic plants expressing the mutant AtCULl proteins, all exhibited reduced responses to jasmonate. We also demonstrate that ax6 have an enhanced effect on coil-2 in JA responses, implying a genetic interaction between COI1 and AtCULl in JA signaling. Furthermore, we showed that the mutations of AtCULl affect the assembly of COI1 into SCF, thus attenuate the SCFCOI1 formation. In addition, the point mutations in AtCULl were found to cause severe alterations in protein ubiquitylation and genome expression profiles, probably via attenuation of all AtCUL1-based-SCF complexes.