Biology subjects

Ksas, B.

Publications and source records attributed to Ksas, B..

3 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↗

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↗