The transporter Syn PAM71 is located in the plasma membrane and thylakoids, and mediates manganese tolerance in Synechocystis PCC6803.

Manganese (Mn) is an essential constituent of photosystem II ( PSII) and therefore indispensable for oxygenic photosynthesis. Very little is known about how Mn is transported, delivered and retained in photosynthetic cells. Recently, the thylakoid-localized transporter PAM71 has been linked to chloroplast Mn homeostasis in Arabidopsis thaliana. Here, we characterize the function of its homolog in Synechocystis (Syn PAM71)., We used a loss-of-function line ( ΔSyn PAM71), wild-type ( WT) cells exposed to Mn stress and strains expressing a tagged variant of Syn PAM71 to characterize the role of Syn PAM71 in cyanobacterial Mn homeostasis., The ΔSyn PAM71 strain displays an Mn-sensitive phenotype with reduced levels of chlorophyll and PSI accumulation, defects in PSII photochemistry and intracellular Mn enrichment, particularly in the thylakoid membranes. These effects are attributable to Mn toxicity, as very similar symptoms were observed in WT cells exposed to excess Mn. Moreover, CyanoP, which is involved in the early steps of PSII assembly, is massively upregulated in ΔSyn PAM71. Syn PAM71 was detected in both the plasma membrane and, to a lesser extent, the thylakoid membranes., Our results suggest that Syn PAM71 is involved in the maintenance of Mn homeostasis through the export of Mn from the cytoplasm into the periplasmic and luminal compartments, where it can be stored without interfering with cytoplasmic metabolic processes. [ABSTRACT FROM AUTHOR]