Manganese (Mn) plays a wealth of roles in living systems.It is ubiquitously involved in the antioxidant response because of its ability to catalyze the dismutation of superoxide anions.In eukaryotic cells,Mn also plays a role in protein glycosylation in the secretory system.However,arguably,in photosynthetic organisms,the most important role of Mn is in the oxygen evolving complex at photosystem Ⅱ (PS Ⅱ).At the global level,atmospheric oxygen is derived from the splitting of water,a reaction that relies strictly on the tetra-manganese cluster (Mn4O5Ca) bound to photosystem Ⅱ at the lumen side of the thylakoid membrane.The unique redox properties of this cluster allow the storage of oxidation potential arising from the successive absorption of four photons.This high oxidation potential is required for the energetically highly demanding reaction oxidizing water into molecular oxygen and protons.Achieving this reaction within a plant cell requires efficient manganese import into the chloroplast and further into the thylakoid lumen.Until recently,the molecular mechanisms allowing Mn import into plastids had been completely unknown.Two articles published this year provide the first candidates for the long sought pathway for Mn transport into plastids (Eisenhut et al.,2018;Zhang et al.,2018).
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