The transition metal manganese （Mn） is indispensable for photoautotrophic growth since photosystem II （PSII） employs an inorganic Mn4CaOs cluster for water splitting. Here, we show that the Arabidopsis membrane pr...The transition metal manganese （Mn） is indispensable for photoautotrophic growth since photosystem II （PSII） employs an inorganic Mn4CaOs cluster for water splitting. Here, we show that the Arabidopsis membrane protein CHLOROPLAST MANGANESE TRANSPORTER1 （CMT1） is involved in chloroplast Mn homeostasis. CMT1 is the closest homolog of the previously characterized thylakoid Mn transporter PHOTOSYNTHESIS-AFFECTED MUTANT71 （PAM71）. In contrast to PAM71, CMT1 resides at the chloro- plast envelope and is ubiquitously expressed. Nonetheless, like PAM71, the expression of CMT1 can also alleviate the Mn-sensitive phenotype of yeast mutant qomrl. The cmtl mutant is severely suppressed in growth, chloroplast ultrastructure, and PSII activity owing to a decrease in the amounts of pigments and thylakoid membrane proteins. The importance of CMT1 for chloroplast Mn homeostasis is demonstratedby the significant reduction in chloroplast Mn concentrations in cmtl-1, which exhibited reduced Mn binding in PSII complexes. Moreover, CMT1 expression is downregulated in Mn-surplus conditions. The pam71 cmtl-ldouble mutant resembles the cmtl-f single mutant rather than pare71 in most respects. Taken together, our results suggest that CMT1 mediates Mn2 uptake into the chloroplast stroma, and that CMT1 and PAM71 function sequentially in Mn delivery to PSII across the chloroplast envelope and the thylakoid membrane.展开更多
文摘The transition metal manganese （Mn） is indispensable for photoautotrophic growth since photosystem II （PSII） employs an inorganic Mn4CaOs cluster for water splitting. Here, we show that the Arabidopsis membrane protein CHLOROPLAST MANGANESE TRANSPORTER1 （CMT1） is involved in chloroplast Mn homeostasis. CMT1 is the closest homolog of the previously characterized thylakoid Mn transporter PHOTOSYNTHESIS-AFFECTED MUTANT71 （PAM71）. In contrast to PAM71, CMT1 resides at the chloro- plast envelope and is ubiquitously expressed. Nonetheless, like PAM71, the expression of CMT1 can also alleviate the Mn-sensitive phenotype of yeast mutant qomrl. The cmtl mutant is severely suppressed in growth, chloroplast ultrastructure, and PSII activity owing to a decrease in the amounts of pigments and thylakoid membrane proteins. The importance of CMT1 for chloroplast Mn homeostasis is demonstratedby the significant reduction in chloroplast Mn concentrations in cmtl-1, which exhibited reduced Mn binding in PSII complexes. Moreover, CMT1 expression is downregulated in Mn-surplus conditions. The pam71 cmtl-ldouble mutant resembles the cmtl-f single mutant rather than pare71 in most respects. Taken together, our results suggest that CMT1 mediates Mn2 uptake into the chloroplast stroma, and that CMT1 and PAM71 function sequentially in Mn delivery to PSII across the chloroplast envelope and the thylakoid membrane.
