Biology subjects

Havaux, M.

Publications and source records attributed to Havaux, M..

6 recordsLinked to original sources

bioRxiv2025

Guanosine tetraphosphate (ppGpp) signalling promotes high-light tolerance in Arabidopsis thaliana.

Guanosine tetraphosphate (ppGpp) is a hyperphosphorylated nucleotide originally discovered in prokaryotes and found in the chloroplasts of plants and algae. In plants, ppGpp signalling plays a role as a regulator of photosynthetic activity, which is important in acclimation to environmental stresses such as nitrogen limitation. However, the full range of stresses involving ppGpp signalling is not yet known. Here, we investigated the role of ppGpp accumulation in the acclimation of plants to high light. We found that the over-accumulation of ppGpp in transgenic lines that overexpress RSH3 (OX:RSH3) increases tolerance to high light intensity. Although ppGpp leads to higher non-photochemical energy dissipation (NPQ) than in wild-type plants, we show that NPQ is not critical for the enhanced high-light tolerance. Rather, our results show that ppGpp accumulation leads to broad changes in plant physiology that prime plants to resist and subsequently recover from high light exposure. ppGpp levels themselves also increase in response to high light exposure, suggesting that ppGpp signalling may play a physiological role in high light acclimation. Our work highlights the importance of ppGpp signalling in plant stress acclimation.

plant biology↗

bioRxiv2024

A cytochrome P450 involved in apocarotenoid signaling enhances plant photosynthetic capacity and photooxidative stress tolerance

{beta}-cyclocitric acid and its precursor {beta}-cyclocitral are signaling apocarotenoids which trigger defense and detoxification mechanisms enhancing plant tolerance to abiotic stresses. From a transcriptomic analysis of Arabidopsis plants exposed to each apocarotenoid over several exposure times, we identified a gene (CYP81D11) encoding a cytochrome P450 that is strongly induced under all conditions and is under the control of the TGAII-SCL14 transcription regulator. Overexpressing the CYP81D11 gene in Arabidopsis led to a very tolerant phenotype to high light stress while a CYP81D11- deficient mutant was photosensitive. The transcriptomic profile of the CYP81D11 overexpressor revealed a selective upregulation of genes related to photosynthesis and the response to high light stress. Photosynthetic electron transport, CO2 fixation and biomass production were noticeably improved by high expression levels of CYP81D11. These effects occurred in high light, not in low light, and were associated with a noticeable reduction of singlet oxygen photoproduction. These findings indicate that CYP81D11 is a key component of {beta}-cyclocitral-induced stress tolerance, acting through enhancement of the photosynthetic capacity of leaves. This gene could be a new target for improving photosynthesis, particularly in sunny environments.

plant biology↗

bioRxiv2023

An SMR cell-cycle inhibitor inducible by a carotenoid metabolite resets root development and drought tolerance in Arabidopsis

New regulatory functions in plant development and environmental stress responses have recently emerged for a number of apocarotenoids produced by enzymatic or non-enzymatic oxidation of carotenoids. {beta}-cyclocitric acid ({beta}-CCA) is one such compound derived from {beta}-carotene which triggers defense mechanisms leading to a marked enhancement of plant tolerance to drought stress. We show here that this response is associated with an inhibition of root growth affecting both root cell elongation and division. Remarkably, {beta}-CCA selectively induced cell cycle inhibitors of the SIAMESE-RELATED (SMR) family, especially SMR5, in root tip cells. Overexpression of the SMR5 gene in Arabidopsis induced molecular and physiological changes that mimicked in large part the effects of {beta}-CCA. In particular, the SMR5 overexpressors exhibited an inhibition of root development and a marked increase in drought tolerance which is not related to stomatal closure. SMR5 up-regulation induced changes in gene expression that strongly overlapped with the {beta}-CCA-induced transcriptomic changes. Both {beta}-CCA and SMR5 led to a down-regulation of many cell cycle activators (cyclins, cyclin-dependent kinases) and a concomitant up-regulation of genes related to water deprivation, cellular detoxification and biosynthesis of lipid biopolymers such as suberin and lignin. This was correlated with an accumulation of suberin lipid polyesters in the roots and a decrease in non-stomatal leaf transpiration. Taken together, our results identify the {beta}-CCA-and drought-inducible SMR5 gene as a key component of a stress signaling pathway that reorients root metabolism from growth to multiple defense mechanisms leading to drought tolerance.

plant biology↗

bioRxiv2021

A ppGpp-mediated brake on photosynthesis is required for acclimation to nitrogen limitation in Arabidopsis.

Guanosine pentaphosphate and tetraphosphate (together referred to as ppGpp) are hyperphosphorylated nucleotides found in bacteria and the chloroplasts of plants and algae. In plants and algae artificial ppGpp accumulation can inhibit chloroplast gene expression, and influence photosynthesis, nutrient remobilisation, growth, and immunity. However, it is so far unknown whether ppGpp is required for abiotic stress acclimation in plants. Here, we demonstrate that ppGpp biosynthesis is necessary for acclimation to nitrogen starvation in Arabidopsis. We show that ppGpp is required for remodeling the photosynthetic electron transport chain to downregulate photosynthetic activity and for protection against oxidative stress. Furthermore, we demonstrate that ppGpp is required for coupling chloroplastic and nuclear gene expression during nitrogen starvation. Altogether, our work indicates that ppGpp is a pivotal regulator of chloroplast activity for stress acclimation in plants.

plant biology↗

bioRxiv2021

Manipulation of carotenoid metabolism stimulates biomass and stress tolerance in tomato

Improving yield, nutritional value and tolerance to abiotic stress are major targets of current breeding and biotechnological approaches that aim at increasing crop production and ensuring food security. Metabolic engineering of carotenoids, the precursor of Vitamin-A and plant hormones that regulate plant growth and response to adverse growth conditions, has been mainly focusing on provitamin A biofortification or the production of high-value carotenoids. Here, we show that the introduction of a single gene of the carotenoid biosynthetic pathway in different tomato cultivars simultaneously improved photosynthetic capacity and tolerance to various abiotic stresses (e.g., high light, salt, and drought), caused an up to 77% fruit yield increase and enhanced fruits provitamin A content and shelf life. Our findings pave the way for developing a new generation of crops that combine high productivity and increased nutritional value with the capability to cope with climate change-related environmental challenges.

plant biology↗

bioRxiv2018

β-cyclocitric acid: a new apocarotenoid eliciting drought tolerance in plants

{beta}-Cyclocitral ({beta}-CC) is a volatile compound deriving from 1O2 oxidation of {beta}-carotene in plant leaves. {beta}-CC elicits a retrograde signaling, modulating 1O2-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that {beta}-CC is largely converted into {beta}-cyclocitric acid ({beta}-CCA) in leaves and that this metabolite is a signal involved in stress tolerance. Treatment of Arabidopsis plants with {beta}-CCA markedly enhanced plant tolerance to drought by a mechanism different from known responses such as stomatal closure, changes in osmotic potential and jasmonate signaling. Furthermore, we show that the response to {beta}-CCA does not fully overlap with the {beta}-CC-dependent signaling, indicating that {beta}-CCA induces only a branch of the {beta}-CC signaling pathway. In addition, the protective effect of {beta}-CCA is a conserved mechanism, being observed in a variety of plant species. This study provides a new bioactive agent with promising agronomic applications for protecting plants against drought.

plant biology↗