Biology subjects

Huleux, M.

Publications and source records attributed to Huleux, M..

4 recordsLinked to original sources

bioRxiv2024

DYRKP kinase regulates cell wall degradation in Chlamydomonas by inducing matrix metalloproteinase expression

The cell wall of plants and algae is an important cell structure that protects cells from changes in the external physical and chemical environment. This extracellular matrix composed of polysaccharides and glycoproteins, is needed to be remodeled continuously throughout the life cycle. However, compared to matrix polysaccharides, little is known about the mechanisms regulating the formation and degradation of matrix glycoproteins. We report here that a plant kinase belonging to the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family present in all eukaryotes regulates cell wall degradation in the model microalga Chlamydomonas reinhardtii by inducing the expression of matrix metalloproteinases (MMPs). In the absence of DYRKP, daughter cells fail to degrade the parental cell wall, and form multicellular structures. On the other hand, the complementation line of DYRKP was shown to degrade the parental cell wall normally. Transcriptomic and proteomic analyses indicate a marked down-regulation of MMP expression in the dyrkp mutants. Additionally, the expression of MMP was confirmed to be consistent with the expression pattern of DYRKP. Our findings show that DYRKP, by ensuring timely MMP expression, enables the successful execution of the cell cycle. Altogether, this study provides new insight into the life cycle regulation in plants and algae. IN A NUTSHELLO_ST_ABSBackgroundC_ST_ABSPlants and algae have different types of polysaccharides in their cell walls, but they have glycoproteins in common. Glycoprotein synthesis and degradation must be tightly regulated to ensure normal growth and differentiation. However, little is known about the regulatory mechanism of glycoprotein degradation in both plants and algae. The cell cycle of Chlamydomonas reinhardtii begins anew with the hatching of daughter cells, and the role of matrix metalloproteinases (MMPs) is known to be important in this process. In our previous study, we observed that a knockout mutant of the plant kinase belonging to the dual-specificity tyrosine phosphorylation-regulated kinase (DYRKP) formed a palmelloid structure and failed to hatch. QuestionsWhat is the role of DYRKP in microalgae? Specifically, why does the dyrkp mutant form a palmelloid structure? Palmelloid is usually observed in dividing cells or after exposure to stresses. We therefore hypothesized that the palmelloid phenotype observed in dyrkp mutant could either be due to a defect in cell hatching or due to an increased stress state in the mutant population. FindingsWe answered these questions by comparative studies in different culture conditions and by examining additional dyrkp knockout mutants generated by CRISPR-Cas9 in various background strains with more or less intact cell walls. Palmelloid formation in the dyrkp mutant was observed under optimal growth (mixo- or auto-trophic condition) and very low light conditions. Interestingly, unlike the parent strain, in which only cell wall fragments are observed in old cultures, the parental cell wall of the dyrkp mutant remained almost intact even after the release of daughter cells. Also, the cell division rate of the cell wall-less dyrkp mutants was similar to their background strain. These results suggest that dyrkp mutants have a problem in degrading the parental cell walls. Indeed, proteomic and transcriptomic analyses revealed reduced levels of protease families in the dyrkp mutant, and in particular with a significantly lower amount of several key members of the MMP family. Through the analysis of complementation lines, we confirmed that the DYRKP was required for strong and rapid expression of MMPs. Next stepsWe are pursuing research to understand what the phosphorylation clients of DYRKP are and how they regulate the expression of the MMPs identified in this study. One sentence summaryThe DYRKP kinase induces the expression of matrix metalloproteinases involved in the degradation of the parental cell wall, allowing prompt hatching of daughter cells after cell division.

plant biology↗

bioRxiv2023

The α/β hydrolase domain-containing protein 1 (ABHD1) acts as a lysolipid lipase and is involved in lipid droplet formation

Lipid droplets (LDs) are the major sites of lipid and energy homeostasis. However, few LD biogenesis proteins have been identified. Here, using Chlamydomonas as a model, we show that ABHD1, a member of the /{beta} hydrolase domain-containing protein family, is a novel type of LD-associated protein which stimulates LD formation through two distinct actions on the LD surface, one enzymatic and the other structural. ABHD1 was localized to LD surface in Chlamydomonas cells. The knockout mutants contained similar amounts of triacylglycerols (TAG) but their LDs showed an increased content in lyso- derivatives of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine (DGTS). Over-expression of ABHD1 in Chlamydomonas induced LD formation and boosted TAG content, suggesting a key role in LD biogenesis. The purified recombinant ABHD1 protein hydrolyzed lyso-DGTS, producing a free fatty acid and a glyceryltrimethylhomoserine moiety. In vitro experiments using droplet- embedded vesicles showed that ABHD1 promoted LD emergence. Taken together, these results identify ABHD1 as a new player in LD formation by its lipase activity on lyso-DGTS and by its distinct biophysical property. This study further suggests that lipases targeted to LDs and able to act on their polar lipid coat may be interesting tools to promote LD assembly in eukaryotic cells. Significant statementLipid droplets are subcellular organelles specialized for triacylglycerol storage. Their dynamic turnover is key to managing energy homeostasis in response to cell cycle states and environmental cues. To gain insights into LD biogenesis, we characterized a putative /{beta}- hydrolase (ABHD1) in the model algae Chlamydomonas reinhardtii and show it is located at the LD surface. We found that ABHD1 overexpression promotes LD formation and acts as a lipase mainly on lyso derivatives of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine (DGTS), the major lipid constituent of the LD hemi-membrane. We also show that ABHD1 has a remarkable biophysical property favoring LD budding. This work thus identifies a novel type of lipase acting on betaine lipid and provides a first example of a protein with a dual function nvolved in LD formation.

biochemistry↗

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↗

bioRxiv2022

Boosting chloroplast ribosome biogenesis by a plastidial DEAD-box RNA helicase is critical for high light acclimation

Photosynthetic organisms have developed sophisticated strategies to fine-tune light energy conversion to meet the metabolic demand, thereby optimizing growth in fluctuating light environments. Although mechanisms such as energy dissipation, photosynthetic control, or the photosystem II (PSII) damage and repair have been widely studied, little is known about the regulation of protein synthesis capacity during light acclimation. By screening a Chlamydomonas reinhardtii insertional mutant library using chlorophyll fluorescence imaging, we isolated a high chlorophyll fluorescence mutant (hf0) defected in a gene encoding a putative plastid targeted DEAD-box RNA helicase called CreRH22. CreRH22 is rapidly induced upon illumination and belongs to the GreenCut, a set of proteins specific to photosynthetic organisms. While photosynthesis is slightly affected in the mutant under low light (LL), exposure to high light (HL) induces a marked decrease in both PSII and PSI, and a strong alteration of the light-induced gene expression pattern. These effects are explained by the inability of hf0 to increase plastid ribosome amounts under HL. We conclude that CreRH22, by promoting ribosomal RNA precursor maturation in a light-dependent manner, enables the assembly of extra-ribosomes required to synthesize photosystem subunits at a higher rate, a critical step in the acclimation of algae to HL.

plant biology↗