Domain architecture of plant eukaryotic translation initiation factor 3 subunit E governs interaction with translational <i>cis</i> -elements to regulatepollen tube growth

An octameric eukaryotic translation initiation factor 3 subunit E (eIF3E) preserves translational homeostasis through selective messenger RNA (mRNA) recognition and ribosome assembly. Yet, the mechanisms by which eIF3E maintains translational equilibriumremain poorly understood. We show here that eIF3E domain architecture and phosphorylation sites (Thr417, Ser421) are conserved across eukaryotes. Deleting the Proteasome-COP9 signalosome-Initiation factor 3 domain (PCI domain) abolished nuclear localization, disrupted eIF3E-eIF3L interaction, and impaired eIF3E dissociation from the polysomes. Affnity RNA immunoprecipitation sequencing of eIF3E::YFP in tobacco pollen tubes identified mRNAs bearing coding-sequence motifs (MC1 to MC3) that co-immunoprecipitate with eIF3E.Using mRNA reporter assay, we reveal that these motifs act in tandem as eIF3E-dependent translational repressors and enhancers. AlphaFold3 structural modeling and Förster resonance energy transfer verification indicate that PCI domain deletion or PCI-phosphosite mutagenesis weaken eIF3E-eIF3L interactions and block translational activation of MC2 RNA reporter. We further show thatloss of the PCI domain or PCI-phosphosite mutagenesis misregulate pollen tube growth and membrane organization. Together, our findings underscore eIF3E as a selective regulator of mRNA translation that couplescis-motifrecognition to membrane integrityand pollen tube growth, thereby ensuringplant fertility.