A Mediator–transcription factor module that regulates fruit ripening in tomato

Deng, Yang, Li, Chang, Sun et al. explore the interaction between EIN3-like transcription factors and subunits of the Mediator complex in tomato fruit ripening.

Background: Fruit ripening relies on the precise spatiotemporal control of RNA polymerase II (Pol II)-dependent transcription of thousands of ripening-related genes, including regulatory genes and structural genes. In tomato, ethylene is a key signal that regulates fruit ripening. As the master regulators of the ethylene signaling pathway, ETHYLENE INSENSITIVE3 (EIN3)/EIN3-LIKE (EIL) transcription factors play a critical role in fruit ripening. In addition to EILs, a plethora of transcription factors essential for ripening have been identified. The mechanisms underlying the communication between key transcription factors and the Pol II general transcriptional machinery remain largely unknown.

Question: Mediator is an evolutionarily conserved multi-subunit complex that links gene-specific transcriptional factors with Pol II transcriptional machinery. It is unclear which subunit is involved in the transcriptional regulation of tomato fruit ripening.

Findings: We found that the Mediator subunit MED25 physically interacts with EILs, thereby orchestrating an ethylene-dependent transcriptional program for the regulation of ripening-induced gene expression. We demonstrated that MED25 forms a transcriptional module with EILs to regulate the expression of ripening-related regulatory as well as structural genes through promoter binding. We also showed that the EIL1–MED25 module orchestrates both positive and negative feedback transcriptional circuits, along with its downstream regulators, to fine-tune ethylene homeostasis during fruit ripening.

Next steps: One interesting direction for future exploration is to elucidate the functional significance and role of the EIL–MED25-dependent hierarchical transcriptional cascade in regulating fruit ripening.

Reference:

Lei Deng, Tianxia Yang, Qian Li, Zeqian Chang, Chuanlong Sun, Hongling Jiang, Xianwen Meng, Tingting Huang, Chang-Bao Li, Silin Zhong, Chuanyou Li (2023) Tomato MED25 regulates fruit ripening by interacting with EIN3-like transcription factors. https://doi.org/10.1093/plcell/koac349