Intelligent image-activated sorting of Chlamydomonas reinhardtii by mitochondrial localization

Dramatic Changes in Mitochondrial Subcellular Location and Morphology Accompany Activation of the CO2 Concentrating Mechanism

Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for ~50% of global photosynthesis, compartmentalize their Rubisco into a specialized structure known as the pyrenoid when the cells experience limiting CO2 conditions; this compartmentalization appears to be a component of the CO2 Concentrating Mechanism (CCM), which facilitates photosynthetic CO2 fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO2 limiting conditions, although a role for this reorganization in CCM function remains unclear. We used the green microalgae Chlamydomonas reinhardtii to monitor changes in the position and ultrastructure of mitochondrial membranes as cells transition between high CO2 (HC) and Low/Very Low CO2 (LC/VLC). Upon transferring cells to VLC, the mitochondria move from a central to a peripheral location, become wedged between the plasma membrane and chloroplast envelope, and mitochondrial membranes orient in parallel tubular arrays that extend from the cell's apex to its base. We show that these ultrastructural changes require protein and RNA synthesis, occur within 90 min of shifting cells to VLC conditions, correlate with CCM induction and are regulated by the CCM master regulator CIA5. The apico-basal orientation of the mitochondrial membrane, but not the movement of the mitochondrion to the cell periphery, is dependent on microtubules and the MIRO1 protein, which is involved in membrane-microtubule interactions. Furthermore, blocking mitochondrial electron transport in VLC acclimated cells reduces the cell's affinity for inorganic carbon. Overall, our results suggest that CIA5-dependent mitochondrial repositioning/reorientation functions in integrating cellular architecture and energetics with CCM activities and invite further exploration of how intracellular architecture can impact fitness under dynamic environmental conditions.

Chemical synthesis of left arm of Chlamydomonas reinhardtii mitochondrial genome and in vivo functional analysis

Chlamydomonas reinhardtii is a photosynthetic eukaryote showing great industrial potential. The synthesis and in vivo function of the artificial C. reinhardtii genome not only promotes the development of synthetic biology technology but also supports industries that utilize this algae. Mitochondrial genome (MtG) is the smallest and simplest genome of C. reinhardtii that suits synthetic exploration. In this article, we designed and assembled a synthetic mitochondria left arm (syn-LA) genome sharing >92% similarity to the original mitochondria genome (OMtG) left arm, transferred it into the respiratory defect strain cc-2654, screened syn-LA containing transformants from recovered dark-growth defects using PCR amplification, verified internal function of syn-LA via western blot, detected heteroplasmic ratio of syn-LA, tried promoting syn-LA into homoplasmic status with paromomycin stress, and discussed the main limitations and potential solutions for this area of research. This research supports the functionalization of a synthetic mitochondrial genome in living cells. Although further research is needed, this article nevertheless provides valuable guidance for the synthesis of eukaryotic organelle genomes and opens possible directions for future research.

Mitochondria and chloroplasts function in microalgae energy production

Microalgae are organisms that have the ability to perform photosynthesis, capturing CO₂ from the atmosphere to produce different metabolites such as vitamins, sugars, lipids, among others, many of them with different biotechnological applications. Recently, these microorganisms have been widely studied due to their possible use to obtain clean energy. It has been postulated that the growth of microalgae and the production of high-energy metabolites depend on the correct function of cellular organelles such as mitochondria and chloroplasts. Thus, the development of different genetic tools to improve the function of these organelles is of high scientific and technological interest. In this paper we review the recent advances in microalgae engineering and the role of cellular organelles in order to increase cell productivity and biomass.