Wheat Type One Protein Phosphatase Participates in the Brassinosteroid Control of Root Growth via Activation of BES1.

Brassinosteroids (BRs) play key roles in diverse plant growth processes through a complex signaling pathway. Components orchestrating the BR signaling pathway include receptors such as kinases, transcription factors, protein kinases and phosphatases. The proper functioning of the receptor kinase BRI1 and the transcription factors BES1/BZR1 depends on their dephosphorylation by type 2A protein phosphatases (PP2A). In this work, we report that an additional phosphatase family, type one protein phosphatases (PP1), contributes to the regulation of the BR signaling pathway. Co-immunoprecipitation and BiFC experiments performed in Arabidopsis plants overexpressing durum wheat TdPP1 showed that TdPP1 interacts with dephosphorylated BES1, but not with the BRI1 receptor. Higher levels of dephosphorylated, active BES1 were observed in these transgenic lines upon BR treatment, indicating that TdPP1 modifies the BR signaling pathway by activating BES1. Moreover, ectopic expression of durum wheat TdPP1 lead to an enhanced growth of primary roots in comparison to wild-type plants in presence of BR. This phenotype corroborates with a down-regulation of the BR-regulated genes CPD and DWF4. These data suggest a role of PP1 in fine-tuning BR-driven responses, most likely via the control of the phosphorylation status of BES1.The authors acknowledge the Tunisian Ministry of Higher Education and Research for funding, and the National Agency for Research Promotion (ANPR) for the financial management of the PRIMA Project GENDIBAR. This work was also supported by the Ministerio de Economía y Competitividad, co-financed by the European Regional Development Fund (grant BIO2017-82609-R to M.A.B and V.A-S). Mariem Bradai was granted by Mujeres por Africa and from COST INDEPTH Action (COST CA16212, 2017)

The art of painting chromosome loops

How to get a metre of DNA into a tiny space while preserving its functional characteristics? This question seems easy to pose, but the answer is far from being trivial. Facing this riddle, salvation came from technical improvements in microscopy and in situ hybridisation techniques applied to cytogenetics. Here, we would like to look into the past at one of these pure cytogenetics articles that makes a breakthrough in addressing this question in plant science. Our choice fell on the work published two decades ago by Fransz et al. (2002). Besides the elegant manner in which DNA probes were organised to bring into light the out-looping arrangement of interphase chromosomes in Arabidopsis thaliana nuclei, this article perfectly illustrates that painting is not reserved to the fine art. As for whether emotional expression prioritised by artists can sometimes hide behind scientific empirical evidence, there is only a small step to make to the general case

UV-C response of the ribonucleotide reductase large subunit involves both E2F-mediated gene transcriptional regulation and protein subcellular relocalization in tobacco cells

E2F factors are implicated in various cellular processes including specific gene induction at the G(1)/S transition of the cell cycle. We present in this study a novel regulatory aspect for the tobacco large subunit of ribonucleotide reductase (R1a) and its encoding gene (RNR1a) in the UV-C response. By structural analyses, two E2F sites were identified on the promoter of this gene. Functional analysis showed that, in addition to their role in the specific G(1)/S induction of the RNR1a gene, both E2F sites were important for regulating specific RNR1a gene expression in response to UV-C irradiation in non-synchronized and synchronized cells. Concomitantly, western blot and cellular analyses showed an increase of a 60 kDa E2F factor and a transient translocation of a GFP-R1a protein fusion from cytoplasm to nucleus in response to UV irradiation

Is the plant nucleus a mechanical rheostat?

International audienceBeyond its biochemical nature, the nucleus is also a physical object. There is accumulating evidence that its mechanics plays a key role in gene expression, cytoskeleton organization, and more generally in cell and developmental biology. Building on data mainly obtained from the animal literature, we show how nuclear mechanics may orchestrate development and gene expression. In other words, the nucleus may play the additional role of a mechanical rheostat. Although data from plant systems are still scarce, we pinpoint recent advances and highlight some differences with animal systems. Building on this survey, we propose a list of prospects for future research in plant nuclear mechanotransduction and development

Mechanical Shielding in Plant Nuclei

International audienceBeyond its biochemical nature, the nucleus is also a physical object. There is accumulating evidence that its mechanics plays a key role in gene expression, cytoskeleton organization, and more generally in cell and developmental biology. Building on data mainly obtained from the animal literature, we show how nuclear mechanics may orchestrate development and gene expression. In other words, the nucleus may play the additional role of a mechanical rheostat. Although data from plant systems are still scarce, we pinpoint recent advances and highlight some differences with animal systems. Building on this survey, we propose a list of prospects for future research in plant nuclear mechanotransduction and development

Ribonucleotide Reductase Regulation in Response to Genotoxic Stress in Arabidopsis1[W]

Ribonucleotide reductase (RNR) is an essential enzyme that provides dNTPs for DNA replication and repair. Arabidopsis (Arabidopsis thaliana) encodes three AtRNR2-like catalytic subunit genes (AtTSO2, AtRNR2A, and AtRNR2B). However, it is currently unclear what role, if any, each gene contributes to the DNA damage response, and in particular how each gene is transcriptionally regulated in response to replication blocks and DNA damage. To address this, we investigated transcriptional changes of 17-d-old Arabidopsis plants (which are enriched in S-phase cells over younger seedlings) in response to the replication-blocking agent hydroxyurea (HU) and to the DNA double-strand break inducer bleomycin (BLM). Here we show that AtRNR2A and AtRNR2B are specifically induced by HU but not by BLM. Early AtRNR2A induction is decreased in an atr mutant, and this induction is likely required for the replicative stress checkpoint since rnr2a mutants are hypersensitive to HU, whereas AtRNR2B induction is abolished in the rad9-rad17 double mutant. In contrast, AtTSO2 transcription is only activated in response to double-strand breaks (BLM), and this activation is dependent upon AtE2Fa. Both TSO2 and E2Fa are likely required for the DNA damage response since tso2 and e2fa mutants are hypersensitive to BLM. Interestingly, TSO2 gene expression is increased in atr versus wild type, possibly due to higher ATM expression in atr. On the other hand, a transient ATR-dependent H4 up-regulation was observed in wild type in response to HU and BLM, perhaps linked to a transient S-phase arrest. Our results therefore suggest that individual RNR2-like catalytic subunit genes participate in unique aspects of the cellular response to DNA damage in Arabidopsis