GoKawiilSalicylic acid (SA) is a key phytohormone that activates plant defense responses 1-3. In Arabidopsis, NPR1 (also known as NIM1) and NPR3/NPR4 have been identified as dual SA receptors responsible for perceiving SA 4-6. However, the mechanisms of how SA binding to the NPR proteins leads to induction of defense gene expression remain unclear. Here, we elucidate how SA triggers transcriptional activation via NPR1 and relieves transcriptional repression mediated by NPR3/NPR4. We identified Mediator Complex Subunit 15A (MED15A) as a bridge between NPR1 and the Mediator complex governing transcription. SA induces direct interaction of NPR1 with MED15A. Structural and functional analysis showed that the binding of NPR1 to MED15A is essential for NPR1-mediated transcriptional activation. Meanwhile, SA relieves transcriptional repression mediated by NPR3/NPR4. NIM1-interacting 1 (NIMIN1) interacts with NPR3/NPR4 and the Topless (TPL) co-repressor, connecting them to Polycomb Repressive Complex 2 (PRC2) to mediate H3K27 trimethylation of SA-responsive genes. SA inhibits the interactions between NPR3/NPR4 and NIMIN1, reduces H3K27 trimethylation levels and increases histone acetylation of the target genes to release NPR3/NPR4-mediated repression. Our study offers a comprehensive view of SA-mediated defense gene activation. These findings lay a foundation for designing more effective SA analogs as agrochemicals and for engineering crop resistance by manipulating SA perception and signaling.
Mechanisms of Transcriptional Regulation by Salicylic Acid Receptors
Why This Matters
This research uncovers the molecular mechanism by which salicylic acid triggers plant immune responses, revealing how NPR1 activates and NPR3/NPR4 repress defense genes at the transcriptional level. Understanding this dual-receptor system could enable the development of improved agrochemicals and genetically engineered crops with enhanced disease resistance, which matters for agricultural biotechnology and food security.
Key Takeaways
- NPR1 activates defense genes by directly binding MED15A, a bridge to the transcription-regulating Mediator complex, upon salicylic acid signaling.
- NPR3/NPR4 repress defense genes via NIMIN1, TPL co-repressor, and PRC2, which adds repressive H3K27 trimethylation marks; salicylic acid disrupts this repression.
- These insights into salicylic acid perception and signaling could guide the design of new agrochemicals and crop engineering strategies to boost plant disease resistance.
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