Biology subjects

Menand, B.

Publications and source records attributed to Menand, B..

4 recordsLinked to original sources

bioRxiv2023

Post-translational regulation of photosynthetic activity via the TOR kinase in plants.

Chloroplasts are the powerhouse of the plant cell, yet they are resource-intensive and will cause photooxidative damage if their activity overshoots the demands of growth. The adjustment of chloroplast activity to match growth is therefore vital for stress acclimation. Here we identify a novel post-translational mechanism linking the conserved eukaryotic TOR kinase that promotes growth and the guanosine tetraphosphate (ppGpp) signaling pathway of prokaryotic origin that regulates chloroplast activity, and photosynthesis in particular. We show that RelA SpoT Homologue 3 (RSH3), a nuclear-encoded chloroplastic enzyme responsible for ppGpp biosynthesis, interacts directly with the TOR complex via a plant-specific N-terminal region (NTR) which is hyper-phosphorylated in a TOR-dependent manner. Downregulation of TOR activity reduces NTR phosphorylation, enhances ppGpp synthesis by RSH3, and causes a ppGpp-dependent decrease in photosynthetic capacity. Altogether we demonstrate that the TOR-RSH3 signaling axis is a novel and direct post-translational mechanism that allows chloroplast activity to be matched with plant growth, setting a new precedent for the regulation of organellar function by TOR. One sentence summaryThe TOR kinase post-translationally controls guanosine tetraphosphate signaling to regulate plant photosynthetic activity.

plant biology↗

bioRxiv2021

Guanosine tetraphosphate (ppGpp) accumulation inhibits chloroplast gene expression and promotes super grana formation in the moss Physcomitrium (Physcomitrella) patens

The nucleotides guanosine tetraphosphate and pentaphosphate (or ppGpp) are implicated in the regulation of chloroplast function in plants. ppGpp signalling is best understood in the model vascular plant Arabidopsis thaliana where it acts to regulate plastid gene expression to influence photosynthesis, plant development and immunity. However, little is known about the conservation or diversity of ppGpp signaling in other land plants. Here, we studied the function of ppGpp in the moss Physcomitrium (previously Physcomitrella) patens using an inducible system for triggering ppGpp accumulation. We used this approach to investigate the effects of ppGpp on chloroplast function, photosynthesis and growth. We demonstrate that ppGpp accumulation causes a dramatic drop in photosynthetic capacity by inhibiting chloroplast gene expression. This was accompanied by the unexpected reorganisation of the thylakoid system into super grana. Surprisingly, these changes did not affect gametophore growth, suggesting that bryophytes and vascular plants may have different tolerances to defects in photosynthesis. Our findings point to the existence of both highly conserved and more specific targets of ppGpp signalling in the land plants that may reflect different growth strategies.

plant biology↗

bioRxiv2020

ppGpp influences protein protection, growth and photosynthesis in Phaeodactylum tricornutum

O_LIChloroplasts retain elements of a bacterial stress response pathway that is mediated by the signalling nucleotides guanosine penta- and tetraphosphate, or (p)ppGpp. In the model flowering plant Arabidopsis, ppGpp acts as a potent regulator of plastid gene expression and influences photosynthesis, plant growth and development. However, little is known about ppGpp metabolism or its evolution in other photosynthetic eukaryotes. C_LIO_LIHere, we studied the function of ppGpp in the diatom P. tricornutum using transgenic lines containing an inducible system for ppGpp accumulation. We used these lines to investigate the effects of ppGpp on growth, photosynthesis, lipid metabolism and protein expression. C_LIO_LIWe demonstrate that ppGpp accumulation reduces photosynthetic capacity and promotes a quiescent-like state with reduced proliferation and ageing. Strikingly, using non-targeted proteomics, we discovered that ppGpp accumulation also leads to the coordinated upregulation of a protein protection response in multiple cellular compartments. C_LIO_LIOur findings highlight the importance of ppGpp as a fundamental regulator of chloroplast function across different domains of life, and lead to new questions about the molecular mechanisms and roles of (p)ppGpp signalling in photosynthetic eukaryotes. C_LI

plant biology↗

bioRxiv2018

Golden magic: RSH enzymes for (p)ppGpp metabolism in the diatom Phaeodactylum tricornutum.

The nucleotides guanosine tetraphosphate and pentaphosphate (together known as (p)ppGpp or magic spot) are produced in plant plastids from GDP/GTP and ATP by RelA-SpoT homologue (RSH) enzymes. In the model plant Arabidopsis (p)ppGpp regulates chloroplast transcription and translation to affect growth, and is also implicated in acclimation to stress. However, little is known about (p)ppGpp metabolism or its evolution in other photosynthetic eukaryotes. Here we studied (p)ppGpp metabolism in the golden-coloured marine diatom Phaeodactylum tricornutum. We identified three expressed RSH genes in the P. tricornutum genome, and determined the enzymatic activity of the corresponding enzymes by heterologous expression in bacteria. We showed that two P. tricornutum RSH are (p)ppGpp synthetases, despite substitution of a residue within the active site believed critical for activity, and that the third RSH is a bifunctional (p)ppGpp synthetase and hydrolase, the first of its kind demonstrated in a photosynthetic eukaryote. A broad phylogenetic analysis then showed that diatom RSH belong to novel algal RSH clades. Together our work significantly expands the horizons of (p)ppGpp signalling in the photosynthetic eukaryotes by demonstrating an unexpected functional, structural and evolutionary diversity in RSH enzymes from organisms with plastids derived from red algae.\n\nHighlightWe discover RSH enzymes for (p)ppGpp metabolism in the diatom Phaeodactylum tricornutum and show that they have surprising functional and structural features, and belong to novel red-plastid lineage RSH clades.

plant biology↗