Biology subjects

Guerard, F.

Publications and source records attributed to Guerard, F..

5 recordsLinked to original sources

bioRxiv2025

CP12 controls ribulose 1,5 bisphosphate recycling and carbon acquisition in Chlamydomonas reinhardtii

The small chloroplastic protein CP12 has multiple functions, including the regulation of enzymes in the Calvin-Benson-Bassham cycle. Here, we investigated its role in the acclimation of Chlamydomonas reinhardtii to varying CO2 availability. This alga has a CO2 concentrating mechanism that increases the supply of CO2 to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and involves hallmarks such as HCO3- transporters and carbonic anhydrases as well as the condensation of RuBisCO within the pyrenoid via its interaction with a scaffold protein named Essential Pyrenoid Component 1 (EPYC1). We showed that compared to the wild type, at high CO2, C. reinhardtii CP12 deletion mutants, or partially complemented mutants, have less phosphoribulokinase and ribulose-1,5-bisphosphate (RuBP) indicating that the regeneration of RuBP is regulated by CP12. In the absence of CP12, the expected relocation of RuBisCO towards the pyrenoid was not observed upon transition from high to very low CO2, contrary to WT cells. The CP12 deletion mutants are a unique example where the induction of CO2 concentrating mechanism hallmarks at very low CO2 was not accompanied by RuBisCO relocation. Altogether, these results suggest that CP12 contributes to the coordination between RuBP regeneration, RuBisCO location and CO2 acquisition. HighlightCP12 regulates phosphoribulokinase amount and its product RuBP. The CP12 deletion mutants are unique example where the RuBisCO location was not correlated with the induction of CO2 concentration mechanism. This reveals a novel link between Calvin-Benson-Bassham cycle regulation and CO2 concentrating mechanisms in Chlamydomonas reinhardtii. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/659560v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1cdadb2org.highwire.dtl.DTLVardef@46ae27org.highwire.dtl.DTLVardef@538295org.highwire.dtl.DTLVardef@a214c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Maize (Zea mays L.) interaction with the arbuscular mycorrhizal fungus Rhizophagus irregularis allows mitigation of nitrogen deficiency stress: physiological and molecular characterization

Maize is currently the most productive cereal crop in the world (www.faostat.org). Maize can form a symbiotic relationship with the Arbuscular Mycorrhizal Fungus (AMF), Rhizophagus irregularis. In this relationship, the fungus provides the plant with additional water and mineral nutrients, while the plant supplies carbon compounds to the fungus. Little is known about the N metabolism disruption during symbiosis in both partners. To address this issue, two genetically distant maize lines were studied in terms of physiological and molecular responses to AMF inoculation by dual RNA-seq, metabolomics and phenotyping. Interestingly, the beneficial effects of the AMF were observed mainly under conditions of limited N fertilization. Under such conditions, the AMF helped maintain plant biomass production. The availability of nitrogen was found to be a crucial factor influencing all the traits studied showing that the level of N supply plays a pivotal role in determining how maize plants interact with the AMF. Despite the two maize lines showing different transcriptomic and metabolomic responses to R. irregularis, their agro-physiological traits remained similar. Both the plant and fungal transcriptomes were more significantly influenced by the level of N nutrition rather than the specific maize genotype. This suggests that N availability has a more profound impact on gene expression in both organisms than the genetic makeup of the maize plant. To understand the metabolic implications of this symbiotic relationship, we integrated transcriptomic data into our recently built multi-organ Genome-scale metabolic model (GSM) called iZMA6517. Remarkably, this modelling approach was supported by metabolomics profiling, in particular increased leaf pyrimidine levels in response to AMF inoculation under limiting N supply. Consistently, fungal genes involved in pyrimidine de novo synthesis and salvage were found to be expressed in symbiotic roots. Our work highlights nucleotide and ureides metabolism as previously unrecognized factors contributing to the symbiotic N nutrition facilitated by R. irregularis, thereby enhancing maize growth. This study demonstrates the effectiveness of integrating multi-omics approaches with mathematical modelling to uncover novel metabolic mechanisms associated with AM symbiosis, without a priori.

plant biology↗

bioRxiv2022

Manganese excess and deficiency affects photosynthesis and metabolism in Marchantia polymorpha

Manganese is an essential metal for plant growth. The most important Mn-containing enzyme is the Mn4CaO5 cluster that catalyses water oxidation in Photosystem II. Mn deficiency primarily affects photosynthesis, while Mn excess is generally toxic. Mn excess and deficiency were studied in the liverwort Marchantia polymorpha, an emerging model ideally suited for analysis of metal stress since it accumulates rapidly toxic substances due to the absence of well-developed vascular and radicular systems and a reduced cuticle. We established growth conditions for Mn excess and deficiency, performed analysis of metal content in thalli and isolated chloroplasts and determined metabolites. Metabolome analysis revealed a strong accumulation of N-methylalanine upon exposure to Mn excess and a different response of Marchantia to heavy metal stress than that known for higher plants. We investigated photosynthetic performance by chlorophyll fluorescence at room temperature and at 77K, P700 absorption and by studying the susceptibility of thalli to photoinhibition. In vivo super-resolution fluorescence microscopy was used to visualize changes in the organization of the thylakoid membrane under Mn excess and deficiency. Non-optimal Mn concentrations changed the ratio of photosystem I to photosystem II and altered the organisation of thylakoid membranes. Mn deficiency seems to favour cyclic electron flow around photosystem I protecting thereby photosystem II against photoinhibition.

plant biology↗

bioRxiv2020

Hexose fluxes, mediated by vacuolar SWEET transporters, are important for xylem development in the inflorescence stem of Arabidopsis thaliana.

In higher plants, the development of the vascular system is controlled by a complex network of transcription factors. However, how nutrient availability in the vascular cells affects their development remains to be addressed. At the cellular level, cytosolic sugar availability is regulated mainly by sugar exchanges at the tonoplast through active and/or facilitated transport. In Arabidopsis thaliana, among the tonoplastic transporters, SWEET16 and SWEET17 genes have been previously localized in the vascular system. Here, using a reverse genetic approach, we propose that sugar exchanges at the tonoplast, regulated by SWEET16, are important for xylem cell division as revealed in particular by the decreased number of xylem cells in the swt16 mutant and the expression of SWEET16 at the procambium-xylem boundary. In addition, we demonstrate that transport of hexoses mediated by SWEET16 and/or SWEET17 is required to sustain the formation of the xylem secondary cell wall. This result is in line with a defect in the xylem cell wall composition as measured by FTIR in the swt16swt17 double mutant and by upregulation of several genes involved in secondary cell wall synthesis. Our work therefore supports a model in which xylem development is partially dependent on the exchange of hexoses at the tonoplast of xylem-forming cells.

plant biology↗

bioRxiv2020

Bradyrhizobium diazoefficiens USDA110 nodulation of Aeschynomene afraspera is associated with atypical terminal bacteroid differentiation and suboptimal symbiotic efficiency

Legume plants can form root organs called nodules where they house intracellular symbiotic rhizobium bacteria. Within nodule cells, rhizobia differentiate into bacteroids, which fix nitrogen for the benefit of the plant. Depending on the combination of host plants and rhizobial strains, the output of rhizobium-legume interactions is varying from non-fixing associations to symbioses that are highly beneficial for the plant. Bradyrhizobium diazoefficiens USDA110 was isolated as a soybean symbiont but it can also establish a functional symbiotic interaction with Aeschynomene afraspera. In contrast to soybean, A. afraspera triggers terminal bacteroid differentiation, a process involving bacterial cell elongation, polyploidy and membrane permeability leading to loss of bacterial viability while plants increase their symbiotic benefit. A combination of plant metabolomics, bacterial proteomics and transcriptomics along with cytological analyses was used to study the physiology of USDA110 bacteroids in these two host plants. We show that USDA110 establish a poorly efficient symbiosis with A. afraspera, despite the full activation of the bacterial symbiotic program. We found molecular signatures of high level of stress in A. afraspera bacteroids whereas those of terminal bacteroid differentiation were only partially activated. Finally, we show that in A. afraspera, USDA110 bacteroids undergo an atypical terminal differentiation hallmarked by the disconnection of the canonical features of this process. This study pinpoints how a rhizobium strain can adapt its physiology to a new host and cope with terminal differentiation when it did not co-evolve with such a host. ImportanceLegume-rhizobium symbiosis is a major ecological process in the nitrogen cycle, responsible for the main input of fixed nitrogen in the biosphere. The efficiency of this symbiosis relies on the coevolution of the partners. Some legume plants, but not all, optimize their return-on-investment in the symbiosis by imposing on their microsymbionts a terminal differentiation program that increases their symbiotic efficiency but imposes a high level of stress and drastically reduce their viability. We combined multi-omics with physiological analyses to show that the non-natural symbiotic couple formed by Bradyrhizobium diazoefficiens USDA110 and Aeschynomene afraspera is functional but displays a low symbiotic efficiency associated to a disconnection of terminal bacteroid differentiation features.

microbiology↗