Bioenergetics in microalgae : regulation modes of mitochondrial respiration, photosynthesis, and fermentative pathways, and their interactions in secondary algae.
A MAGIC design to study photosynthesis and nutrient homeostasis in Chlamydomonas reinhardtii
Towards a better sunlight to biomass conversion efficiency in microalgae
Respiratory chain comprises four major complexes that transfer electrons from NADH and succinate to molecular oxygen, at least one alternative oxidase and several NAD(P)H dehydrogenases. Electron transfer through complexes I, III and IV is coupled to the generation of a proton gradient (pmf or proton motive force) which is consumed by complex V (F1Fo ATP synthase) to synthesize ATP. In Chlamydomonas, more than one hundred components of the chain have been identified (Cardol et al., 2005) thanks to the sequencing of the nuclear and mitochondrial genomes of the alga (Merchant et al., 2007).
The researches of our lab are focusing on the characterization of components involved in the biogenesis of the respiratory complexes. We are also intested in the interaction between photosynthesis and respiration.
Part of our efforts are devoted to the characterization of complex I. This complex is the less understood of all the enzymes of the respiratory chain, mainly because of its large size. By combining genomic and proteomic approaches, we have identified at least 42 subunits in Chlamydomonas complex I (Cardol et al., 2004). Except for ND2, all the mitochondria-encoded subunits (ND1, ND4, ND5 and ND6) have been inactivated by random mutagenesis (Cardol et al., 2002; Remacle et al., 2001; Cardol et al., 2008) or site-drected mutagenesis (Remacle et al., 2006; Larosa et al., 2011). We have extended our work to ND3 and ND4L nucleus-encoded subunits, by using the RNA interference technique to silent the expression of the genes (Cardol et al., 2006).
We are also exploring the structure of complex IV and are trying to elucidate the role of some chaperones involved in the delivery of copper to the enzyme. The mitochondrial mutants and suppressors that we have isolated by far were made by random mutagenesis with acriflavin (Remacle et al., 2004; Remacle et al., 2001). However, site-directed mutagenesis of the mitochondrial DNA would represent a valuable tool. In collaboration with Dr Nathalie Bonnefoy (CGM, Gif-sur-Yvette, France), we are now trying to set up a method to efficiently transform Chlamydomonas mitochondria in order to introduce point mutations in respiratory genes present on the mitochondrial DNA of the alga.