Different partners, different roles!

You et al. show that LEUNIG_HOMOLOG Facilitates Jaresponses via interactions with the histone acetyltransferase HAC1 and the Mediator complex coactivator MED25.   Plant Cell https://doi.org/10.1105/tpc.19.00115

By Yanrong You and Chuanyou Li, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China

Background: Jasmonate (JA) is a lipid-derived plant hormone that regulates plant defense responses against mechanical wounding, herbivore attack, and pathogen infection. MYC2 is a master transcription factor that regulates diverse aspects of JA responses. At low JA levels, repressor JASMONATE ZIM DOMAIN (JAZ) proteins recruit the Groucho (Gro)/Tup1 family corepressor TOPLESS (TPL) to inhibit MYC2-dependent activation of JA-responsive genes. Following hormone-dependent degradation of JAZ repressors, MYC2 is released. The Mediator complex is an evolutionarily conserved multisubunit coactivator complex whose activity is essential for RNA polymerase II (Pol II)-dependent gene transcription in eukaryotic cells. Mediator subunit MED25 interacts directly with MYC2 and is involved in the assembly of a MYC2-MED25 functional transcription complex (MMC) during hormone-triggered activation of MYC2.

Questions: Are there are some new components of this MMC that help MED25 to activate MYC2’s transcriptional activity upon hormone perception? What are the molecular mechanisms of hormone-dependent activation of MYC2?.

Findings: In contrast to TPL, which represses MYC2 in the resting stage, we found that two other Gro/Tup1 family of corepressors, LEUNIG (LUG) and LEUNIG_HOMOLOG (LUH), are new components of the MMC, and they redundantly activate MYC2 upon hormone elicitation. LUH activates MYC2-directed transcription of JA-responsive genes via the Mediator complex coactivator and the histone acetyltransferase HAC1. MED25 directly recruits LUH to MYC2 target promoters, and then LUH links MYC2 with HAC1-dependent histone H3K9 acetylation to activate JA-responsive genes. We also found that LUH acts as a scaffold to coordinate the coactivators MED25 and HAC1 during JA-triggered activation of MYC2. Considering the role of TPL, our study demonstrates that different members of the plant Gro/Tup1 family play antagonistic roles in regulating the same signaling pathway through distinct mechanisms.

Next steps: One interesting direction for future exploration is to identify the epigenetic partners of LUG and to elucidate their mechanisms of action during the activation of MYC2. Furthermore, our finding that LUH activates JA signaling can be exploited for improving the resistance of crop plants.

Yanrong You, Qingzhe Zhai, Chunpeng An, Chuanyou Li (2019). LEUNIG_HOMOLOG Mediates Jasmonate-Dependent Transcriptional Activation in Cooperation with the Coactivators HAC1 and MED25. Plant Cell. https://doi.org/10.1105/tpc.19.00115.

Key words: Jasmonate, MYC2, LUH, Coactivator