Chemocarrier-Enabled Peptide Inhibition of MYC-Cofactor Interactions in Plants.

Direct chemical inhibition of transcription factor (TF)-cofactor interactions in plants remains challenging because their large protein-protein interfaces are poorly suited to conventional small molecules, while peptide-based inhibitors are limited by inefficient intracellular delivery. In our previous work, we demonstrated that peptide inhibitors can disrupt MYC transcription factor complexes in plants, but only at relatively high concentrations. Here, we show that a chemically defined chemocarrier overcomes this limitation and enables low-dose functional activity of peptide inhibitors in planta. To access TF-cofactor interfaces, we established a multi-step, target-guided screening platform that links in vitro high-throughput assays with functional validation in plants. This workflow integrates primary and secondary AlphaScreen assays using full-length and truncated MYC constructs with a tertiary assay targeting the interaction between MYCs and the MED25 coactivator. Screening of an approved-drug library followed by structure-activity optimization led to the identification of a low-toxicity aromatic derivative with potent cell-penetrating activity in Arabidopsis. Conjugation with this chemocarrier markedly enhanced the intracellular delivery and functional efficacy of multiple MYC-targeting peptide scaffolds, including cyclic and stapled peptides, resulting in over two orders of magnitude improvement in potency. This enabled robust inhibition of MYC-dependent transcriptional programs at substantially reduced concentrations, converting peptide-based inhibition from a high-dose proof-of-concept into a low-dose, functionally tractable strategy. These findings establish a practical chemical modality for accessing transcription factor-cofactor interfaces in plants.