Biology subjects

Moussu, S.

Publications and source records attributed to Moussu, S..

5 recordsLinked to original sources

bioRxiv2023

A pectin-binding peptide with a structural and signaling role in the assembly of the plant cell wall

Pressurized cells with strong walls make up the hydrostatic skeleton of plants. Assembly and expansion of such stressed walls depend on a family of secreted RAPID ALKALINIZATION FACTOR (RALF) peptides which, curiously, bind both a membrane receptor complex and wall-localized LEUCINE-RICH REPEAT EXTENSINs (LRXs) in a mutually exclusive way. Here we show that, in root hairs, the RALF22 peptide has a dual structural and signaling role in cell expansion. Together with LRX1, it directs the compaction of charged pectin polymers at the root hair tip into periodic circumferential rings. Free RALF22 induces the formation of a complex with LORELEI-LIKE-GPI-ANCHORED PROTEIN 1 (LLG1) and FERONIA (FER), triggering adaptive cellular responses. These findings show how a peptide simultaneously functions as a structural component organizing cell wall architecture and as a signaling molecule that regulates this process. This mechanism may also underlie wall assembly and expansion in other plant cell types.

plant biology↗

bioRxiv2019

Structural basis for recognition of RALF peptides by LRX proteins during pollen tube growth

Plant reproduction relies on the highly regulated growth of the pollen tube for proper sperm delivery. This process is controlled by secreted RALF signaling peptides, which have been previously shown to be perceived by CrRLK1Ls membrane receptor-kinases and leucine-rich (LRR) extensin proteins (LRXs). Here we demonstrate that RALF peptides are active as folded, disulfide bond-stabilized proteins, which can bind to the LRR domain of LRX proteins with nanomolar affinity. Crystal structures of the LRX-RALF signaling complexes reveal LRX proteins as constitutive dimers. The N-terminal LRR domain containing the RALF binding site is tightly linked to the extensin domain via a cysteine-rich tail. Our biochemical and structural work reveals a complex signaling network by which RALF ligands may instruct different signaling proteins - here CrRLK1Ls and LRXs - through structurally different binding modes to orchestrate cell wall remodeling in rapidly growing pollen tubes.\n\nSignificancePlant reproduction relies on proper pollen tube growth to reach the female tissue and release the sperm cells. This process is highly regulated by a family of secreted signaling peptides that are recognized by cell-wall monitoring proteins to enable plant fertilization. Here, we report the crystal structure of the LRX-RALF cell-wall complex and we demonstrate that RALF peptides are active as folded proteins. RALFs are autocrine signaling proteins able to instruct LRX cell-wall modules and CrRKL1L receptors, through structurally different binding modes to coordinate pollen tube integrity.

plant biology↗

bioRxiv2018

A stress-response-related inter-compartmental signalling pathway regulates embryonic cuticle integrity in Arabidopsis

The embryonic cuticle is necessary for normal seed development and seedling establishment in Arabidopsis. Although mutants with defective embryonic cuticles have been identified, neither the deposition of cuticle material, nor its regulation, has been described during embryogenesis. Here we use electron microscopy, lipid staining and permeability assays to show that cuticle deposition initiates de novo in patches on globular embryos. By combining these techniques with genetics and gene expression analysis, we show that successful patch coalescence to form a continuous cuticle requires a signalling involving the endosperm-specific subtilisin protease ALE1 and the receptor kinases GSO1 and GSO2, which are expressed in the developing embryonic epidermis. Transcriptome analysis shows that this pathway regulates stress-related gene expression in seeds. Consistent with these findings we show genetically, and through activity analysis, that the stress-associated MPK6 protein acts downstream of GSO1 and GSO2 in the developing embryo. We propose that a stress-related signalling pathway has been hijacked in some angiosperm seeds through the recruitment of endosperm-specific components. Our work reveals the presence of an inter-compartmental dialogue between the endosperm and embryo that ensures the formation of an intact and functional cuticle around the developing embryo through an \"auto-immune\" type interaction.

plant biology↗

bioRxiv2018

From spatio-temporal morphogenetic gradients to rhythmic patterning at the shoot apex

Rhythmic patterning is central to the development of eukaryotes, particularly in plant shoot post-embryonic development. The plant hormone auxin drives rhythmic patterning at the shoot apical meristem, but the spatio-temporal dynamics of the auxin gradients is unknown. We used quantitative imaging to demonstrate that auxin provides high-definition graded information not only in space but also in time. We provide evidence that developing organs are auxin-emitting centers that could self-organize spatio-temporal auxin gradients through a transport network converging on the meristem center. We further show that a memory of the exposition of cells to auxin allows to differentiate temporally sites of organ initiation, providing a remarkable example of how the dynamic redistribution of a morphogenetic regulator can be used to create rhythmicity.

plant biology↗

bioRxiv2018

Crystal structures of two tandem malectin-like receptor kinases involved in plant reproduction

A complex cell-to-cell communication between the male pollen tube and the female reproductive organs is required for plant fertilization. A family of Catharanthus roseus Receptor Kinase-1 ( CrRLK1L) membrane receptors has been genetically implicated in this process. Here we present crystal structures of the CrRLK1Ls ANXUR1 and 2 at 1.48 and 1.1 [A] resolution, respectively. Our structures reveal a novel arrangement of two malectin-like domains connected by a short {beta}hairpin linker and stabilized by calcium ions. The canonical carbohydrate interaction surfaces of related animal and bacterial carbohydrate binding modules are not conserved among plant CrRLK1Ls. In line with this, we failed to detect binding of chemically diverse oligosaccharides to ANXUR1 and HERCULES1. Instead, CrRLK1Ls have evolved a protein-protein interface between their malectin domains, which forms a deep cleft lined by highly conserved aromatic and polar residues. Analysis of the glycosylation pattern of different CrRLK1Ls and their oligomeric states together suggests that this cleft could resemble a binding site for a ligand required for CrRLK1Ls receptor activation.

plant biology↗