Annexin 5 is a key player in orchestrating the pollen sequestrome

Like dry seeds, mature pollen grains store a large reservoir of RNA species that enables rapid activation and germination under favorable conditions. The molecular mechanisms governing the accumulation of these RNA reservoirs remain poorly understood. Here, we show that the Arabidopsis pollen-specific protein annexin 5 (ANN5) localizes to the nucleolus and exerts dose-dependent control over ribosome biogenesis, as evidenced by altered steady-state rRNA levels in mature pollen. Ectopic expression of ANN5 also induced the accumulation of translationally repressed RNA in plant somatic tissues. Mechanistically, ANN5 interacts with histone deacetylase 2B (HD2B) and nucleolin (NUC1), which are known epigenetic modulators of ribosome biogenesis. In metabolically active cells, ANN5 associates with ribosomal and ribosome-associated proteins, suggesting it modulates the regulatory landscape of translation. We propose that the primary physiological role of ANN5 is to coordinate the formation and subsequent availability of RNA reserves during pollen maturation and activation.