Biology subjects

Velay, F.

Publications and source records attributed to Velay, F..

3 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↗

bioRxiv2022

Structural Maintenance of Chromosome 3 interacts with the Topoisomerase VI complex and contributes to the oxidative stress response in Arabidopsis thaliana.

In plants adverse environmental conditions can induce the accumulation of reactive oxygen species, such as singlet oxygen or hydrogen peroxide, at the level of the photosynthetic apparatus. The coordinated action of nucleus-encoded genes is required for containing the deleterious effects of reactive oxygen species. The regulation of such genes follows a molecular signalling process between the chloroplast and the nucleus called retrograde signalling. Previously, we proposed that the Topoisomerase VI (Topo VI) complex participates in the singlet oxygen stress response by regulating the expression of specific subsets of nuclear genes. However, the underlying molecular mechanisms remain unresolved. In this study, we demonstrate that the Topo VI subunit BIN4 interacts with the cohesin subunit AtSMC3. We also show that, similarly to Topo VI mutants, a line suppressing AtSMC3 shows constitutive activation of singlet oxygen response genes and enhanced tolerance to photooxidative stress. Together, these results suggest that Topo VI and AtSMC3 control the expression of singlet oxygen response genes and are possibly involved in the acclimation of plants to photooxidative stress conditions.

plant biology↗

bioRxiv2019

Topoisomerase VI participates in an insulator-like function that prevents H3K9me2 spreading into euchromatic islands

The organization of the genome into transcriptionally active and inactive chromatin domains requires well-delineated chromatin boundaries and insulator functions in order to maintain the identity of adjacent genomic loci with antagonistic chromatin marks and functionality. In plants that lack known chromatin insulators, the mechanisms that prevent heterochromatin spreading into euchromatin remain to be identified. Here, we show that DNA Topoisomerase VI participates in a chromatin boundary function that safeguards the expression of genes in euchromatin islands within silenced heterochromatin regions. While some transposable elements are reactivated in mutants of the Topoisomerase VI complex, genes insulated in euchromatin islands within heterochromatic regions of the Arabidopsis thaliana genome are specifically downregulated. H3K9me2 levels consistently increase at euchromatin island loci and decrease at some TE loci. We further show that Topoisomerase VI physically interacts with S-adenosylmethionine (SAM) synthase MAT3, which is required for H3K9me2 deposition. Topoisomerase VI promotes MAT3 occupancy on heterochromatic elements and its exclusion from euchromatic islands, thereby providing a mechanistic insight into the essential role of Topoisomerase VI in the delimitation of chromatin domains.

plant biology↗