Related Papers
The role of BST4 in the pyrenoid ofChlamydomonas reinhardtii
Chun Sing Lau
ABSTRACTIn many eukaryotic algae, CO2 fixation by Rubisco is enhanced by a CO2- concentrating mechanism, which utilizes a Rubisco-rich organelle called the pyrenoid. The pyrenoid is traversed by a network of thylakoid-membranes called pyrenoid tubules, proposed to deliver CO2. In the model algaChlamydomonas reinhardtii(Chlamydomonas), the pyrenoid tubules have been proposed to be tethered to the Rubisco matrix by a bestrophin-like transmembrane protein, BST4. Here, we show that BST4 forms a complex that localizes to the pyrenoid tubules. A Chlamydomonas mutant impaired in the accumulation of BST4 (bst4) formed normal pyrenoid tubules and heterologous expression of BST4 inArabidopsis thalianadid not lead to the incorporation of thylakoids into a reconstituted Rubisco condensate. Chlamydomonasbst4mutant did not show impaired growth at air level CO2. By quantifying the non-photochemical quenching (NPQ) of chlorophyll fluorescence, we show thatbst4displays a transiently lower thylakoid ...
Proceedings of the National Academy of Sciences
Thylakoid localized bestrophin-like proteins are essential for the CO 2 concentrating mechanism of Chlamydomonas reinhardtii
2019 •
Ananya Mukherjee
Significance Models of the CO 2 concentrating mechanism (CCM) of green algae and diatoms postulate that chloroplast CO 2 is generated from HCO 3 − brought into the acidic thylakoid lumen and converted to CO 2 by specific thylakoid carbonic anhydrases. However, the identity of the transporter required for thylakoid HCO 3 − uptake has remained elusive. In this work, 3 bestrophin-like proteins, BST1–3, located on the thylakoid membrane have been found to be essential to the CCM of Chlamydomonas . Reduction in expression of BST1–3 markedly reduced the inorganic carbon affinity of the alga. These proteins are prime candidates to be thylakoid HCO 3 − transporters, a critical currently missing step of the CCM required for future engineering efforts of the Chlamydomonas CCM into plants to improve photosynthesis.
The Plant Cell
A phase-separated CO2-fixing pyrenoid proteome determined by TurboID in Chlamydomonas reinhardtii
Chun Sing Lau
Phase separation underpins many biologically important cellular events such as RNA metabolism, signaling, and CO2 fixation. However, determining the composition of a phase-separated organelle is often challenging due to its sensitivity to environmental conditions, which limits the application of traditional proteomic techniques like organellar purification or affinity purification mass spectrometry to understand their composition. In Chlamydomonas reinhardtii, Rubisco is condensed into a crucial phase-separated organelle called the pyrenoid that improves photosynthetic performance by supplying Rubisco with elevated concentrations of CO2. Here, we developed a TurboID-based proximity labeling technique in which proximal proteins in Chlamydomonas chloroplasts are labeled by biotin radicals generated from the TurboID-tagged protein. By fusing 2 core pyrenoid components with the TurboID tag, we generated a high-confidence pyrenoid proxiome that contains most known pyrenoid proteins, in a...
Journal of Experimental Botany
The Chlamydomonas reinhardtii chloroplast envelope protein LCIA transports bicarbonate in planta
Britta Förster
LCIA (low CO2-inducible protein A) is a chloroplast envelope protein associated with the CO2-concentrating mechanism of the green alga Chlamydomonas reinhardtii. LCIA is postulated to be a HCO3– channel, but previous studies were unable to show that LCIA was actively transporting bicarbonate in planta. Therefore, LCIA activity was investigated more directly in two heterologous systems: an Escherichia coli mutant (DCAKO) lacking both native carbonic anhydrases and an Arabidopsis mutant (βca5) missing the plastid carbonic anhydrase βCA5. Neither DCAKO nor βca5 can grow in ambient CO2 conditions, as they lack carbonic anhydrase-catalyzed production of the necessary HCO3– concentration for lipid and nucleic acid biosynthesis. Expression of LCIA restored growth in both systems in ambient CO2 conditions, which strongly suggests that LCIA is facilitating HCO3– uptake in each system. To our knowledge, this is the first direct evidence that LCIA moves HCO3– across membranes in bacteria and p...
Alternative electron pathways of photosynthesis drive the algal CO2 concentrating mechanism
2021 •
Yonghua Li-Beisson
Global photosynthesis consumes ten times more CO2 than net anthropogenic emissions, and microalgae account for nearly half of this consumption1. The great efficiency of algal photosynthesis relies on a mechanism concentrating CO2 (CCM) at the catalytic site of the carboxylating enzyme RuBisCO, thus enhancing CO2 fixation2. While many cellular components involved in the transport and sequestration of inorganic carbon (Ci) have been uncovered3,4, the way microalgae supply energy to concentrate CO2 against a thermodynamic gradient remains elusive4-6. Here, by monitoring dissolved CO2 consumption, unidirectional O2 exchange and the chlorophyll fluorescence parameter NPQ in the green alga Chlamydomonas, we show that the complementary effects of cyclic electron flow and O2 photoreduction, respectively mediated by PGRL1 and flavodiiron proteins, generate the proton motive force (pmf) required by Ci transport across thylakoid membranes. We demonstrate that the trans-thylakoid pmf is used by...
Plants
Adapting from Low to High: An Update to CO2-Concentrating Mechanisms of Cyanobacteria and Microalgae
Dmitry Los
The intracellular accumulation of inorganic carbon (Ci) by microalgae and cyanobacteria under ambient atmospheric CO2 levels was first documented in the 80s of the 20th Century. Hence, a third variety of the CO2-concentrating mechanism (CCM), acting in aquatic photoautotrophs with the C3 photosynthetic pathway, was revealed in addition to the then-known schemes of CCM, functioning in CAM and C4 higher plants. Despite the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of microalgae and cyanobacteria for the CO2 substrate and low CO2/O2 specificity, CCM allows them to perform efficient CO2 fixation in the reductive pentose phosphate (RPP) cycle. CCM is based on the coordinated operation of strategically located carbonic anhydrases and CO2/HCO3− uptake systems. This cooperation enables the intracellular accumulation of HCO3−, which is then employed to generate a high concentration of CO2 molecules in the vicinity of Rubisco’s active centers compensating up fo...
Proceedings of the National Academy of Sciences
A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle
2016 •
Leif Pallesen
Significance Eukaryotic algae, which play a fundamental role in global CO 2 fixation, enhance the performance of the carbon-fixing enzyme Rubisco by placing it into an organelle called the pyrenoid. Despite the ubiquitous presence and biogeochemical importance of this organelle, how Rubisco assembles to form the pyrenoid remains a long-standing mystery. Our discovery of an abundant repeat protein that binds Rubisco in the pyrenoid represents a critical advance in our understanding of pyrenoid biogenesis. The repeat sequence of this protein suggests elegant models to explain the structural arrangement of Rubisco enzymes in the pyrenoid. Beyond advances in basic understanding, our findings open doors to the engineering of algal pyrenoids into crops to enhance yields.
bioRxiv (Cold Spring Harbor Laboratory)
The phase separated CO2-fixing pyrenoid proteome determined by TurboID
2022 •
Chun Sing Lau
Assembly of the algal CO2-fixing organelle, the pyrenoid, is guided by a Rubisco-binding motif
2020 •
Chun Sing Lau
Approximately one-third of the Earth’s photosynthetic CO2 assimilation occurs in a pyrenoid, an organelle containing the CO2-fixing enzyme Rubisco. How constituent proteins are recruited to the pyrenoid, and how the organelle’s sub-compartments - membrane tubules, a surrounding phase-separated Rubisco matrix, and a peripheral starch sheath - are held together is unknown. Using the model alga Chlamydomonas reinhardtii, we discovered that pyrenoid proteins share a sequence motif. We show that the motif is sufficient to target proteins to the pyrenoid and that the motif binds to Rubisco, suggesting a mechanism for targeting. The presence of the Rubisco-binding motif on proteins that localize to the tubules and on proteins that localize to the matrix-starch sheath interface suggests that the motif holds the pyrenoid’s three sub-compartments together. Our findings advance our understanding of pyrenoid biogenesis and illustrate how a single protein motif can underlie the architecture of a...
Plant Physiology
Carbon Supply and Photoacclimation Cross Talk in the Green Alga Chlamydomonas reinhardtii
2016 •
Iryna Polukhina
