Compartmentalised Function of TaHRC-R Orchestrates ROS Production and Nuclear Condensate Dynamics.

Fhb1 is the most widely used locus for Fusarium head blight (FHB) resistance in wheat, yet the mechanistic basis of its candidate gene, TaHRC, remains elusive. Here, we demonstrate that the protein from the resistant allele TaHRC-R localises to both the nucleus and cytoplasm, whereas the susceptible protein TaHRC-S is confined to the nucleus. Remarkably, only TaHRC-R triggered a reactive oxygen species (ROS) burst in planta, dependent on its extranuclear localisation. The N-terminal 21 amino acids that distinguish TaHRC-R from TaHRC-S were essential for its nuclear export and ROS induction. Within the nucleus, TaHRC-R formed heterodimers with TaHRC-S via its N-terminal 21 amino acids and central region, disrupting the formation of large, sparse TaHRC-S condensates and converting them into numerous smaller assemblies. These results reveal a dual, spatially coordinated mechanism whereby TaHRC-R promotes ROS production outside the nucleus while modulating nuclear condensate dynamics to counteract the susceptible allele. This compartmentalised functionality provides a molecular framework for Fhb1-mediated resistance and illustrates a novel paradigm of subcellular specialisation in plant immunity.