Ferritin is required for rapid remodeling of the photosynthetic apparatus and minimizes photo-oxidative stress in response to iron-availability in Chlamydomonas reinhardtii

Andreas Busch1, Blandine Rimbauld2, Bianca Naumann1, Stefan Rensch2 & Michael Hippler1,2

1Department of Biology, Institute of Plant Biochemistry and Biotechnology, University of MŸnster, Hindenburgplatz 55, 48143 MŸnster, Germany; 2Institute of General Botany and Plant Physiology, University of Jena, Dornburger Str. 159, 07743 Jena, Germany

Ferritin is a key player in the iron-homeostasis due to its ability to store large quantities of iron. Chlamydomonas reinhardtii contains two nuclear genes for ferritin (ferr1 and ferr2) that are constitutively expressed under iron-sufficient conditions and become induced when cells are shifted to iron-deficient conditions. In response to the reduced iron-availability a degradation of photosystem I (PSI) and a remodeling of its light harvesting complex, as described previously, can be seen. This active PSI degradation is slowed down under photo-autotrophic conditions where photosynthesis is indispensable. We observed a strong induction of ferritin that correlated with the degree of PSI degradation during iron deficiency. After iron-repletion the PSI level restore to normal within 24 hours at the expense of the accumulated ferritin. RNAi strains, which are significantly reduced in the ferritin amount, show a striking delay in the degradation of PSI under iron deficiency. Furthermore, these strains are more susceptible to photo-oxidative stress under high-light conditions. We conclude (i) that ferritin is used to buffer the iron released by the degradation of the photosynthetic complexes, (ii) that the physiological status of the cell determines the strategy to cope with iron deficiency, (iii) that the availability of ferritin is important for rapid degradation of PSI under iron deficiency and (iv) that ferritin plays a protective role under photo-oxidative stress conditions.

e-mail address of presenting author: busch.andreas@gmx.net