In vivoproperties of Arabidopsis FCA condensates involved in RNA 3’ processing

Abstract

AbstractOur understanding of the functional requirements underpinning biomolecular condensationin vivois still relatively poor. The Arabidopsis RNA binding protein FCA is found in liquid-like nuclear condensates that function in RNA 3’ processing, promoting proximal polyadenylation at many targets in the Arabidopsis genome. To further understand the properties of these condensatesin vivowe used single particle tracking experiments on FCA stably expressed at endogenous levels in plant nuclei. These revealed FCA forms a core tetramer that multimerizes into higher-order particles, corresponding to condensates observed using confocal microscopy. The coiled-coil protein FLL2, which is genetically required for FCA function and condensate formation, showed co-localization primarily to the larger condensates. A missense mutation in the FCA RRM domain, also identified in a genetic screen, reduced the average FCA condensate size but had no influence on core FCA tetramer formation. Our work points to a modular structure for FCA condensates centred around a core of four FCA molecules, which multimerize to larger functionally important condensates via associated RNA and FLL2 interaction.