NRAMP2 controls manganese partitioning between seed coat and embryo to regulate seed vigor

Seed development and germination depend on the coordinated transport of macronutrients and micronutrients, which sustain the embryo and determine seed vigour. Manganese (Mn) is an essential micronutrient involved in various metabolic processes, yet its role in seed development is not well understood. In this study, we investigated manganese (Mn) homeostasis in seeds and identified NRAMP2, a previously characterised trans-Golgi-localised Mn exporter, as a key transporter that controls Mn delivery to the embryo. Promoter analysis showed NRAMP2 expression in the chalazal region, which is a central hub for the exchange of nutrients between maternal tissues and the developing seed. X-ray fluorescence mapping revealed mislocalisation of Mn in nramp2 mutant seeds, retention of Mn on the seed coat and markedly reduced levels of Mn in the embryo. Functionally, Mn depletion delayed seed germination and increased physiological dormancy by reducing reactive oxygen species (ROS) accumulation. Our results uncover the vital role of Mn in supporting embryo development and seed vigour, establishing NRAMP2 as a pivotal component of the Mn transport machinery during seed development.