Jasmonate-mediated transcriptional regulation and plant defense
Rong Chen, Hongling Jiang and Chuanyou Li^*

State Key Laboratory of Plant Genomics, National Centre for Plant Gene Research (Beijing), Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No. 1 West Beichen Road, Beijing 100101, China.
*Corresponding Author: Tel: (+8610) 6480 6612; Fax: (+8610) 6480 6595; E-mail: cyli@genetics.ac.cn

Abstract
Transcriptional regulation plays a central role in plant hormone signaling. At the core of transcriptional regulation is the Mediator, an evolutionarily conserved, multi-subunit complex that serves as a bridge between gene specific transcription factors and the RNA polymerase machinery to regulate transcription. Here we report the action mechanisms of the MED25 subunit of the Arabidopsis Mediator in regulating jasmonate- and abscisic acid (ABA)-triggered gene transcription. We show that during jasmonate signaling, MED25 physically associates with the bHLH transcription factor MYC2 in promoter regions of MYC2 target genes and exerts a positive effect on MYC2-regulated gene transcription. We also show that MED25 physically associates with the basic leucine zipper transcription factor ABI5 (ABA-INSENSITIVE 5) in promoter regions of ABI5 target genes and shows a negative effect on ABI5-regulated gene transcription. Our results reveal that underlying the distinct effects of MED25 on jasmonate and ABA signaling, the interaction mechanisms of MED25 with MYC2 and ABI5 are different. These results highlight that the MED25 subunit of the Arabidopsis Mediator regulates a wide range of signaling pathways through selectively interacting with specific transcription factors.

Key Words: jasmonate, Mediator complex, transcriptional regulation