Arabidopsis CSN5A Acts as a Transcriptional Co-activator of DREB2C During Seed Germination

摘要

The dehydration-responsive element-binding factor (DREB) family plays an essential role in plant abiotic stress signaling. However, the signaling mechanisms used by DREB-family proteins and their homologs to cooperate with coactivators and activate target-gene transcription are incompletely understood. In this study, yeast two-hybrid (Y2H) screening was performed with the DREB2C DNA-binding domain (DREB2C-N) as bait against an Arabidopsis cDNA library. Subunit 5A of COP9 signalosome (CSN5A) was identified as an interactor and was verified by further Y2H analysis, an in vitro pull-down assay, and an in vivo bimolecular fluorescence complementation assay. Deletion analysis of CSN5A demonstrated that the full-length CSN5A protein was required for interaction with DREB2C-N. Transient co-expression of CSN5A with DREB2C in Arabidopsis protoplasts resulted in significantly increased expression of a DRE-containing HsfA3 promoter fused to the GUS reporter gene (HsfA3-promoter::GUS), indicating that CSN5A acted as a transcriptional co-activator of DREB2C for HsfA3 expression. In addition, CSN5A-overexpression lines exhibited delayed seed germination. Germination delay in CSN5A-overexpressors caused by the interaction of CSN5A with DREB2C leads to an increase in the expression of NCED9, a rate-limiting enzyme for ABA biosynthesis in germinating seeds. Together, these results demonstrate that CSN5A plays a key role as a transcriptional co-activator and regulator of seed germination in Arabidopsis.