| Iron is an essential micronutrient for virtually all living organisms. Because iron has two readily convertible redox states, it is used as a cofactor in bioenergetic reactions such as respiration and photosynthesis. In this work, the molecular mechanisms which allow survival of Chlamydomonas reinhardtii under iron limited conditions were investigated. This includes the characterization of the six isoforms of the abundant iron-containing protein, ferredoxin in Chlamydomonas, the characterization of a putative iron-binding protein involved in cyclic electron flow, Pgrl1, in response to iron deficiency, and a comparison of the effects of iron-limitation on respiration and photosynthesis in the presence and absence of a carbon source. Gene expression analysis and enzyme assays with purified proteins indicate that each ferredoxin isoform in Chlamydomonas is differentially expressed in response to various environmental conditions, and has specificity towards specific substrates, allowing for the more efficient use of ferredoxin. Specifically, I ascribe a role to Fdx2 in nitrate assimilation. The investigation of iron deficiency responses in a pgrl1 RNAi knock-down strain (pgrl1-kd) show that pgrl1-kd cells accumulate more iron than wild-type cells, yet exhibit symptoms of iron deficiency at higher concentrations of iron, suggesting that in addition to mediating cyclic electron flow, Pgrl1 plays a role in iron sensing. Finally, the comparison of iron limitation on photosynthesis and respiration in the presence and absence of a carbon source revealed that iron-limited photoheterotrophic (+acetate) Chlamydomonas maintain high growth rates by sacrificing photosynthesis and prioritizing respiration, while phototrophic (-acetate) cells grow at a slower rate, but accumulate more iron in order to maintain efficient photosynthetic systems throughout the spectrum of iron nutrition. |
