Biology subjects

Nicolet, J.

Publications and source records attributed to Nicolet, J..

4 recordsLinked to original sources

bioRxiv2024

Inositol pyrophosphate catabolism by three families of phosphatases controls plant growth and development

Inositol pyrophosphates (PP-InsPs) are nutrient messengers whose cellular concentration must be tightly regulated. Diphosphoinositol pentakisphosphate kinases (PPIP5Ks) generate the active signaling molecule 1,5-InsP8. PPIP5Ks contain additional phosphatase domains involved in PP-InsP catabolism. Plant and Fungi Atypical Dual Specificity Phosphatases (PFA-DSPs) and NUDIX phosphatases (NUDTs) also hydrolyze PP-InsPs. Here we dissect the relative contributions of the three different phosphatase families to plant PP-InsP catabolism and nutrient signaling. We report the biochemical characterization of inositol pyrophosphate phosphatases from Arabidopsis and Marchantia polymorpha. Overexpression of different PFA-DSP and NUDT enzymes affects PP-InsP levels and leads to stunted growth phenotypes in Arabidopsis. nudt17/18/21 knock-out mutants have altered PP-InsP pools and gene expression patterns, but no apparent growth defects. In contrast, Marchantia polymorpha Mppfa-dsp1ge, Mpnudt1ge and Mpvip1ge mutants display severe growth and developmental phenotypes associated with changes in cellular PP-InsP levels. Analysis of Mppfa-dsp1geand Mpvip1ge supports a role for PP-InsPs in Marchantia phosphate signaling, and additional functions in nitrate homeostasis and cell wall biogenesis. Simultaneous removal of two phosphatase activities enhances the observed growth phenotypes. Taken together, PPIP5K, PFA-DSP and NUDT inositol pyrophosphate phosphatases play important roles in growth and development by collectively shaping plant PP-InsP pools. Author summaryOrganisms must maintain adequate levels of nutrients in their cells and tissues. One such nutrient is phosphorus, an essential building block of cell membranes, nucleic acids and energy metabolites. Plants take up phosphorus in the form of inorganic phosphate and require sufficient cellular phosphate levels to support their growth and development. It has been shown that plants and other eukaryotic organisms "measure" cellular phosphate levels using inositol pyrophosphate signaling molecules. The concentration of inositol pyrophosphates serves as a proxy for the cellular concentration of inorganic phosphate, and therefore inositol pyrophosphate synthesis and degradation must be tightly regulated. Here, we report that three different families of enzymes contribute to the degradation of inositol pyrophosphates in plants. The different phosphatases together shape cellular inositol pyrophosphate pools and thereby affect inorganic phosphate levels. Loss-of-function mutants of the different enzymes display additional defects in nitrate levels and cell wall architecture, suggesting that inositol pyrophosphates regulate cellular processes beyond inorganic phosphate homeostasis.

plant biology↗

bioRxiv2023

Comparisons of two receptor pathways in a single cell-type reveal features of signalling specificity.

To respond appropriately to diverse stimuli, cells harbour numerous receptor pathways yet share downstream signalling components. Mitogen-Activated Protein Kinase (MPK) cascades, present in all eukaryotes, act as central hubs shared amongst diverse signalling pathways. How signalling specificity is maintained within a single plant cell-type is not well understood. We engineered a genetic background for direct comparisons of a developmental and an immunity pathway in the Arabidopsis root endodermis. We show the two pathways maintain distinct outputs despite similar MPK phosphorylation patterns. Systematic activation of all individual MPK Kinases (MKKs) in the endodermis revealed that different MKK groups can drive distinct outputs. We propose that specificity is achieved through a balance of combinatorial activation and cross-pathway inhibition within the MPK cascade. Our findings demonstrate the ability of MPK cascades to generate diverse outputs in one plant cell-type, providing new insights into the mechanisms contributing to signalling specificity.

plant biology↗

bioRxiv2020

Constitutive activation of leucine-rich repeat receptor kinase signaling pathways by BAK1-interacting receptor-like kinase 3 chimera

Receptor kinases with extracellular leucine-rich repeat domains (LRR-RKs) form the largest group of membrane signaling proteins in plants. LRR-RKs can sense small molecule, peptide or protein ligands, and may be activated by ligand-induced interaction with a shape complementary SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) co-receptor kinase. We have previously shown that SERKs can also form constitutive, ligand-independent complexes with the LRR ectodomains of BAK1-interacting receptor-like kinase 3 (BIR3) receptor pseudokinases, negative regulators of LRR-RK signaling. Here we report that receptor chimaera in which the extracellular LRR domain of BIR3 is fused to the cytoplasmic kinase domains of the SERK-dependent LRR-RKs BRASSINOSTEROID INSENSITIVE1, HAESA and ERECTA form tight complexes with endogenous SERK co-receptors in the absence of ligand stimulus. Expression of these chimaera under the control of the endogenous promoter of the respective LRR-RK leads to strong gain-of-function brassinosteroid, floral abscission and stomatal patterning phenotypes, respectively. Importantly, a BIR3-GSO1/SGN3 chimera can partially complement sgn3 Casparian strip formation phenotypes, suggesting that GSO1/SGN3 receptor activation is also mediated by SERK proteins. Collectively, our protein engineering approach may be used to elucidate the physiological functions of orphan LRR-RKs and to identify their receptor activation mechanism in single transgenic lines.

plant biology↗

bioRxiv2018

Mechanistic analysis of the SERK3 elongated allele defines a role for BIR ectodomains in brassinosteroid signaling

The leucine-rich repeat receptor kinase (LRR-RK) BRI1 requires a shape-complementary SERK co-receptor for brassinosteroid sensing and receptor activation. Interface mutations that weaken the interaction between receptor and co-receptor in vitro reduce brassinosteroid signaling responses. The SERK3 elongated (elg) allele maps to the complex interface and shows enhanced brassinosteroid signaling, but surprisingly no tighter binding to the BRI1 ectodomain in vitro. Here, we report that rather than promoting the interaction with BRI1, the elg mutation disrupts the ability of the co-receptor to interact with the ectodomains of BIR receptor pseudokinases, negative regulators of LRR-RK signaling. A conserved lateral surface patch in BIR LRR domains is required for targeting SERK co-receptors and the elg allele maps to the core of the complex interface in a 1.25 [A] BIR3 - SERK1 structure. Collectively, our structural, quantitative biochemical and genetic analyses suggest that brassinosteroid signaling complex formation is negatively regulated by BIR receptor ectodomains.

plant biology↗