Biology subjects

Dao, O.

Publications and source records attributed to Dao, O..

5 recordsLinked to original sources

bioRxiv2025

LCI9 is required for normal pyrenoid starch sheath formation and efficiency of the CO2-concentrating mechanism in Chlamydomonas reinhardtii

O_LIPyrenoid -based CO2-concentrating mechanisms (pCCMs) boost photosynthesis by delivering elevated levels of CO2 to Rubisco. Pyrenoids are often surrounded by a starch sheath thought to enhance pCCM efficiency, but little is known about how the sheath is formed. Here we have assessed the role of the pyrenoid-associate protein LCI9 in starch sheath formation in Chlamydomonas reinhardtii. C_LIO_LIUsing an lci9 mutant we assessed the role of LCI9 in starch sheath morphology by fluorescence and electron microscopy, and its impact on pCCM function by CO2 uptake and growth assays. We determined potential interactors of LCI9 via TurboID proximity labeling. C_LIO_LIIn the absence of LCI9, cells fail to correctly assemble the starch sheath, have lower affinity for inorganic carbon and grow slower under CO2-limiting conditions. LCI9 localises to the starch sheath and is physically close to a range of starch metabolism enzymes and other potential scaffolding proteins. Finally, we show that LCI9 associates with starch in the land plant Arabidopsis thaliana. C_LIO_LILCI9 likely acts as a pyrenoid specific scaffold for starch metabolism enzymes. LCI9 could contribute to ongoing efforts to build a functional pyrenoid in a land plant. C_LI

plant biology↗

bioRxiv2024

Joint operation of the CO2 concentrating mechanism and photorespiration in green algae during acclimation to limiting CO2

Due to low availability of CO2 in aquatic environment, microalgae have evolved a CO2 concentrating mechanism (CCM). It has long been thought that operation of CCM would suppress photorespiration by increasing the CO2 concentration at the Rubisco active site, but experimental evidence is scarce. To better explore the function of photorespiration in algae, we first characterized a Chlamydomonas reinhardtii mutant defected in low-CO2 inducible 20 (LCI20) and show that LCI20 is a chloroplast-envelope glutamate/malate transporter playing a role in photorespiration. By monitoring growth and glycolate excretion in mutants deficient in either CCM or photorespiration, we conclude that: i. CCM induction does not depend on photorespiration, ii. glycolate excretion protects algal cells from the toxicity of unmetabolized photorespiratory intermediates, iii. photorespiration is active at low CO2 when the CCM is operational. This work provides a foundation for a better understanding of the carbon cycle in the ocean where significant glycolate concentrations have been found.

plant biology↗

bioRxiv2023

Algal CO2 capture is powered by alternative electron pathways of photosynthesis

On Earth, microalgae contribute to about half of global net photosynthesis. During photosynthesis, sunlight is converted into chemical energy (ATP and NADPH) used by metabolism to convert CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required for sustaining CO2 fixation, but the relative importance of each pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic and chloroplast to mitochondria electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that each pathway has the potential to energize substantial CO2 fixation, can compensate each other, and that the additional energy requirement to fix CO2 is more than 3 times higher than previous estimations. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast-mitochondria interaction being the most efficient, thus laying bioenergetic foundations for biotechnological improvement of CO2 capture.

plant biology↗

bioRxiv2023

Cyclic and pseudo-cyclic electron pathways play antagonistic roles during nitrogen deficiency in Chlamydomonas reinhardtii

Nitrogen (N) scarcity is a frequently encountered situation that constrains global biomass productivity. In response to N deficiency, cell division stops and photosynthetic electron transfer is downregulated, while carbon storage is enhanced. However, the molecular mechanism downregulating photosynthesis during N deficiency and its relationship with carbon storage are not fully understood. The Proton Gradient Regulator-like 1 (PGRL1) controlling cyclic electron flow (CEF) and Flavodiiron proteins involved in pseudo-(CEF) are major players in the acclimation of photosynthesis. To determine the role of PGRL1 or FLV in photosynthesis under N deficiency, we measured photosynthetic electron transfer, oxygen gas exchange and carbon storage in Chlamydomonas pgrl1 and flvB knockout mutants. Under N deficiency, pgrl1 maintains higher net photosynthesis and O2 photoreduction rates, while flvB shows a similar response compared to control strains. Cytochrome b6f and PSI are maintained at a higher abundance in pgrl1. The photosynthetic activity of flvB and pgrl1 flvB double mutants decreases in response to N deficiency similar to the control strains. Furthermore, the preservation of photosynthetic activity in pgrl1 is accompanied by an increased accumulation of triacylglycerol depending on the genetic background. Taken together, our results suggest that in the absence of PGRL1-controlled CEF, FLV-mediated PCEF maintains net photosynthesis at a high level and that CEF and PCEF play antagonistic roles during N deficiency. It further illustrates how nutrient status and genetic makeup of a strain can affect the regulation of photosynthetic energy conversion in relation to carbon storage and provides new strategies for improving lipid productivity in algae. Significance statementNitrogen (N) deficiency, an often-encountered phenomenon in nature, results in growth arrest, downregulation of photosynthesis and massive carbon storage in microalgae. However, more mechanistic insights involved in tuning photosynthetic electron transfer during N deficiency are required. Here, we provide evidence that a well-conserved protein in chlorophytes, the Proton Gradient Regulator-like 1 (PGRL1), is a key regulator of photosynthesis during N deficiency. In its absence, cells exhibited sustained photosynthesis thanks to the Flavodiiron (FLV) proteins. We propose that both PGRL1 and FLV, by having antagonistic roles in N deficiency, manage the redox landscape, carbon storage and biomass production. Our work revolves around the current paradigm of photosynthesis regulation during N deficiency and provides a new framework for improving biomass production and carbon storage in microalgae for biotechnological purposes.

plant biology↗

bioRxiv2021

Alternative electron pathways of photosynthesis drive the algal CO2 concentrating mechanism

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 bestrophin-like Ci transporters and further establish that a chloroplast-to-mitochondria electron flow contributes to energize non-thylakoid Ci transporters, most likely by supplying ATP. We propose an integrated view of the CCM energy supply network, describing how algal cells distribute photosynthesis energy to power different Ci transporters, thus paving the way to the transfer of a functional algal CCM in plants towards improving crop productivity. One sentence summaryPhotosynthetic alternative electron flows and mitochondrial respiration drive the algal CO2 concentrating mechanism

plant biology↗