# Domain architecture of plant eukaryotic translation initiation factor 3 subunit E governs interaction with translational cis-elements to regulate pollen tube growth

## TL;DR

The study reveals how a protein called eIF3E regulates mRNA translation in plant pollen tubes, impacting cell growth and fertility.

## Contribution

The paper identifies how eIF3E domain architecture and phosphorylation regulate mRNA cis-elements to control pollen tube growth.

## Key findings

- The PCI domain of eIF3E is essential for nuclear localization and interaction with eIF3L.
- eIF3E binds mRNAs with specific coding-sequence motifs (MC1 to MC3) to regulate translation.
- Disruption of the PCI domain or its phosphorylation sites impairs pollen tube growth and membrane organization.

## Abstract

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 equilibrium remain 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 that loss 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 couples cis-motif recognition to membrane integrity and pollen tube growth, thereby ensuring plant fertility.

Translation initiation subunit eIF3E helps balance protein production by coordinating opposing genetic cis-elements, affecting pollen tube growth and the shape of cell membranes.

Graphical AbstractFor image description, please refer to the figure legend and surrounding text.