PABP/purine-rich motif as an initiation module for cap-independent translation in pattern-triggered immunity

Upon stress, eukaryotes typically reprogram their translatome through GCN2-mediated phosphorylation of the eukaryotic translation initiation factor, eIF2a, to inhibit general translation initiation while selectively translating essential stress regulators. Unexpectedly, in plants, pattern-triggered immunity (PTI) and response to other environmental stresses occur independently of the GCN2/eIF2a pathway. Here, we show that while PTI induces mRNA decapping to inhibit general translation, defense mRNAs with a pu-rine-rich element (R-motif) are selectively translated using R-motif as an internal ribosome entry site (IRES). R-motif-dependent translation is executed by poly(A)-binding proteins (PABPs) through preferential association with the PTI-activating eIFiso4G over the repressive eIF4G. Phosphorylation by PTI regulators mitogen-activated protein kinase 3 and 6 (MPK3/6) inhibits eIF4G's activity while enhancing PABP binding to the R-motif and promoting eIFiso4G-mediated defense mRNA translation, establishing a link between PTI signaling and protein synthesis. Given its prevalence in both plants and animals, the PABP/R-motif trans-lation initiation module may have a broader role in reprogramming the stress translatome.

Automated summary

This study reveals that in plants, pattern-triggered immunity (PTI) selectively translates defense mRNAs to respond to environmental stresses through a specific mechanism. The phosphorylation by PTI regulators inhibits general translation initiation while enhancing the translation of defense mRNAs, establishing a link between PTI signaling and protein synthesis.