Mechanisms and regulation of intracellular iron trafficking in Chlamydomonas reinhardtii
Final Report Abstract
The project investigated the role of several proteins in the iron homeostasis and transport inside the cells. Since we encountered major difficulties in the construction of the necessary tools (knock-down mutants and specific antibodies), I focused on the functional characterization of only one protein, ferroportin. The data presented clearly showed that diminished ferroportin expression has a major impact on photoheterotrophic growth under excess iron and high light. This indicates that the absence of ferroportin under iron excess is leading to a disturbed intracellular iron distribution that has a positive impact of growth. The effect of ferroportin depletion on the iron-containing proteins was visible at the level of the two chloroplast ferritins (FER1 and FER2), indicating one more time that ferroportin has an influence on chloroplast iron. We observed as well that FEA1 protein associates with membranes and this membrane associated FEA1 is more abundant in the WT in the first two days of iron starvation. We showed using ferrous-specific molecular probe that the loss of ferroportin leads to a disturbed intracellular ferrous iron distribution when iron concentration is in excess (200 µM Fe-EDTA). Our data indicate the impact on iron-dependent remodeling of PSI under low iron nutrition is less when ferroportin levels are diminished. On the other hand, PSI stability under photoautotrophic high-light conditions is affected when both PGRL1 and FPN1 genes are depleted (in the pgrl1fpn1 mutant). These mutant cells (pgrl1fpn1) showed increased growth sensitivity under all conditions tested (photoautotrophic and photoheterotrophic high, normal and low-light). These data suggest that disturbed intracellular iron distribution and the absence of PGRL1 protein have a great impact on cell growth and PSI stability. Our study on the ferroportin function brings additional information in understanding the iron homeostasis in the alga Chlamydomonas reinhardtii and raises new interesting questions about the link between PGRL1/PGR5 and ferroportin functions in chloroplast iron metabolism.
Publications
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(2015) Copper economy in Chlamydomonas: Prioritized allocation and reallocation of copper to respiration vs. photosynthesis. Proc. Natl. Acad. Sci. 112 (9), 2644-2551
Kropat, J., Gallaher, S.D., Urzica, E.I., Nakamoto, S.S., Strenkert, D., Tottey, S., Mason, A.and Merchant, S.S.
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(2017) Chlamydomonas: Regulation Toward Metal Deficiencies. In: Hippler M. (eds) Chlamydomonas: Molecular Genetics and Physiology. Microbiology Monographs, vol 30. Springer, Cham
Urzica E.I.
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(2017) Identification of methylated GnTI-dependent N-glycans in Botryococcus braunii. New Phytol, 215: 1361–1369
Schulze, S., Urzica, E.I., Reijnders, M. J. M. F., van de Geest, H., Warris, S., Bakker, L. V., Fufezan, C., Martins dos Santos, V. A. P., Schaap, P. J., Peters, S. A. and Hippler, M.
