Upon perception by plant cells, phytohormones trigger genome wide transcriptional reprogramming. Regulated gene expression therefore plays a central role in hormone signaling. At the core of transcriptional regulation is the Mediator, an evolutionarily conserved, multisubunit complex that serves as a bridge between gene-specific transcription factors and the RNA polymerase II machinery to regulate transcription.

While much effort in the field of hormone signaling is devoted to gene-specific transcription factors, the function of the Mediator complex during hormone-triggered gene transcription remains largely unknown. Recent research in Chuanyou Li’s lab brought in-depth understanding on the action mechanisms of MEDIATOR25 （MED25）, a subunit of the Arabidopsis Mediator complex, in regulating JA- and abscisic acid (ABA)-induced gene expression.

They showed that MED25 interacts with the bHLH transcription factor MYC2 and executes a positive effect on MYC2-regulated expression of JA-responsive genes. They also showed that MED25 interacts with the basic domain/Leu zipper (bZIP) transcription factor ABA-INSENSITIVE5 (ABI5) and exerts a negative effect on ABI5-regulated expression of ABA-responsive genes. They provided evidence showing that the conserved activator-interacting domain (ACID) of MED25 is sufficient for its interaction with ABI5 but not sufficient for its interaction with MYC2.

In addition, they revealed that while the putative transcriptional activation domain (TAD) of MYC2 is involved in its interaction with MED25, the TAD domain of ABI5 is not involved in its interaction with MED25.

These findings highlighted that, in response to different hormonal signals, a single plant Mediator subunit can regulate distinct transcriptional programs via interactions with relevant gene-specific transcription factors.

Entitled with “The Arabidopsis Mediator subunit MED25 differentially regulates jasmonate and abscisic acid signaling through interacting with the MYC2 and ABI5 transcription factors”, this work was published recently in The Plant Cell (DOI:10.1105/tpc.112.098277). Graduate Student Rong Chen and Associate Professor Hongling Jiang are co-first authors of this work, which was supported by the Ministry of Agriculture, the Ministry of Science and Technology and National Natural Science Foundation of China.

AUTHOR CONTACT:

Chuanyou Li, Ph.D.

Institute of Genetics and Developmetnal Biology, Chinese Academy of Sciences, Beijing, China.

E-mail: cyli@genetics.ac.cn