摘要
As a key transcription factor in the brassinosteroid (BR) signaling pathway, the activity and expression ofBES1 (BRI1-EMS-SUPPRESSOR 1) are stringently regulated. BES1 degradation is mediated by ubiquitinrelated 26S proteasomal and autophagy pathways, which attenuate and terminate BR signaling;however,the opposing deubiquitinases (DUBs) are still unknown. Here, we showed that the ubp12-2w/13-3 doublemutant phenocopies the BR-deficient dwarf mutant, suggesting that the two DUBs UBP12/UBP13 antagonize ubiquitin-mediated degradation to stabilize BES1. These two DUBs can trim tetraubiquitin with K46 and K63 linkages in vitro. UBP12/BES1 and UBP13/BES1 complexes are localized in bothcytosol and nuclei. UBP12/13 can deubiquitinate polyubiquitinated BES1 in vitro and in planta, andUBP12 interacts with and deubiquitinates both inactive, phosphorylated BES1 and active, dephosphorylated BES1 in vivo. UBP12 overexpression in BES1OE plants significantly enhances cell elongation in hypocotyls and petioles and increases the ratio of leaf length to width compared with BES1OE or UBP12OE plants.Hypocotyl elongation and etiolation result from elevated BES1 levels because BES1 degradation is retardedby UBP12 in darkness or in light with BR. Protein degradation inhibitor experiments show that the majorityof BES1 can be degraded by either the proteasomal or the autophagy pathway, but a minor BES1 fractionremains pathway specific. In conclusion, UBP12/UBP13 deubiquitinate BES1 to stabilize the latter as a positive regulator for BR responses.
基金
This work was supported in part by an RSSS grant(no.NRF-RSSS-002)to N.-H.C.from the National Research Foundation,Singapore.
