Dual role for ubiquitin in plant steroid hormone receptor endocytosis

Brassinosteroids are plant steroid hormones that control many aspects of plant growth and development, and are perceived at the cell surface by the plasma membrane-localized receptor kinase BRI1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Using both artificial ubiquitination of BRI1 and generation of an ubiquitination-defective BRI1 mutant form, we demonstrate that ubiquitination promotes BRI1 internalization from the cell surface and is essential for its recognition at the trans-Golgi network/early endosomes (TGN/EE) for vacuolar targeting. Finally, we demonstrate that the control of BRI1 protein dynamics by ubiquitination is an important control mechanism for brassinosteroid responses in plants. Altogether, our results identify ubiquitination and K63-linked polyubiquitin chain formation as a dual targeting signal for BRI1 internalization and sorting along the endocytic pathway, and highlight its role in hormonally controlled plant development

Essential role for the interaction between hnRNP H/F and a G quadruplex in maintaining p53 pre-mRNA 3′-end processing and function during DNA damage

Following DNA damage, mRNA 3′-end formation is inhibited, contributing to repression of mRNA synthesis. Here we investigated how DNA-damaged cells accomplish p53 mRNA 3′-end formation when normal mechanisms of pre-mRNA 3′-end processing regulation are inhibited. The underlying mechanism involves the interaction between a G-quadruplex structure located downstream from the p53 cleavage site and hnRNP H/F. Importantly, this interaction is critical for p53 expression and contributes to p53-mediated apoptosis. Our results uncover the existence of a specific rescue mechanism of 3′-end processing regulation allowing stress-induced p53 accumulation and function in apoptosis

Carrier Profiling in Si-Implanted Gallium Nitride by Scanning Capacitance Microscopy

International audienceTo face silicon limits, gallium nitride (GaN) exhibits major interests for optoelectronics and power electronic devices. Nevertheless, several challenges have to be overcome, with local doping by ion implantation as a major one. It requires development of reliable characterization tools able to provide electrical information with nanoscale resolution. In this work, Atomic Force Microscopy (AFM) combined to its Scanning Capacitance Microscopy (SCM) mode was used for surface damages quantification and nanoscale dopant profiling. GaN samples have been implanted with Si in order to obtain a box-like profile and annealed above 1000 °C under nitrogen with AlN protective cap layer. SCM measurements have led to reliable and quantitative dopant electrical activity measurements thank to calibration sample. Moreover, a good agreement, in terms of depth and shape, has been obtained between SCM and SIMS profiles. This work has evidenced that a high activation rate of implanted Si can be achieved using rapid thermal annealing

Recent Progresses in GaN Power Rectifier

International audienceIn this work, both “Schottky to Schottky” structure (STS) and pseudo-vertical Schottky barrier diode(pv-SBD) have been processed on GaN heteroepitaxially grown on sapphire or silicon by metal organicchemical vapor deposition (MOCVD) and characterized physically and electrically. Ni and Ti/Al wereused to obtain respectively Schottky and Ohmic contacts using rapid thermal annealing (RTA).Adequate passivation steps and insertion of a resistive guard ring were also implemented in pv-SBD.The STS results, presented in this paper, evidence the impact of the substrate on the growth as wellas all the progresses that have been done on GaN material quality. Furthermore, we demonstrate thathigh quality Schottky diodes can be obtained on GaN grown on sapphire by MOCVD. Indeed, idealityfactors of 1.09 as well as a barrier height of 1.06 eV were obtained on pv-SBD devices that have abreakdown voltage over 600 V

Growth Conditions Determine the DNF2 Requirement for Symbiosis

International audienceRhizobia and legumes are able to interact in a symbiotic way leading to the development of root nodules. Within nodules, rhizobia fix nitrogen for the benefit of the plant. These interactions are efficient because spectacularly high densities of nitrogen fixing rhizobia are maintained in the plant cells. DNF2, a Medicago truncatula gene has been described as required for nitrogen fixation, bacteroid's persistence and to prevent defense-like reactions in the nodules. This manuscript shows that a Rhizobium mutant unable to differentiate is not sufficient to trigger defense-like reactions in this organ. Furthermore, we show that the requirement of DNF2 for effective symbiosis can be overcome by permissive growth conditions. The dnf2 knockout mutants grown in vitro on agarose or Phytagel as gelling agents are able to produce nodules fixing nitrogen with the same efficiency as the wild-type. However, when agarose medium is supplemented with the plant defense elicitor ulvan, the dnf2 mutant recovers the fix- phenotype. Together, our data show that plant growth conditions impact the gene requirement for symbiotic nitrogen fixation and suggest that they influence the symbiotic suppression of defense reactions in nodules

SSR mining in coffee tree EST databases: potential use of EST-SSRs as markers for the Coffea genus

Expressed sequence tags (ESTs) from Coffea canephora leaves and fruits were used to search for types and frequencies of simple sequence repeats (EST-SSRs) with a motif length of 1-6 bp. From a non-redundant (NR) EST set of 5,534 potential unigenes, 6.8% SSR-containing sequences were identified, with an average density of one SSR every 7.73 kb of EST sequences. Trinucleotide repeats were found to be the most abundant (34.34%), followed by di- (25.75%) and hexa-nucleotide (22.04%) motifs. The development of unique genic SSR markers was optimized by a computational approach which allowed us to eliminate redundancy in the original EST set and also to test the specificity of each pair of designed primers. Twenty-five EST-SSRs were developed and used to evaluate cross-species transferability in the Coffea genus. The orthology was supported by the amplicon sequence similarity and the amplification patterns. The > 94% identity of flanking sequences revealed high sequence conservation across the Coffea genus. A high level of polymorphic loci was obtained regardless of the species considered (from 75% for C. liberica to 86% for C. canephora). Moreover, the polymorphism revealed by EST-SSR was similar to that exposed by genomic SSR. It is concluded that Coffea ESTs are a valuable resource for microsatellite mining. EST-SSR markers developed from C. canephora sequences can be easily transferred to other Coffea species for which very little molecular information is available. They constitute a set of conserved orthologous markers, which would be ideal for assessing genetic diversity in coffee trees as well as for cross-referencing transcribed sequences in comparative genomics studies

Si Implanted Reactivation in GaN Grown on Sapphire Using AlN and Oxide Cap Layers

International audienceGallium nitride (GaN) is a promising material for power electronic devices. Due to GaN sensitivity to high temperature treatments, dopant activation, after ion implant, is one of the major critical steps to be overcome. An annealing cap layer is then mandatory during high temperature treatment to avoid degradations. In this work, cap layers, such as AlN and SiOx, were deposited on Si-implanted N-type GaN. Samples were annealed using both classical (FA) and rapid thermal (RTA) annealing for times ranging from 30 s to 8 h and temperatures from 1000 to 1150 °C. Transmission Electron Microscopy has been done to observe the implanted layer structure. After cap layer removal, samples surface has been investigated through Atomic Force Microscopy measurements. Dopant activity was indirectly evaluated by Specific Contact Resistance (SCR) measurements. This work demonstrates that low SCR value (8.2 Â 10À5 X cm2) with low surface roughness ($1 nm) can be reached using RTA and an oxide cap layer. However, presence of hexagonal pits in GaN layer is difficult to avoid. Compromise between low SCR with low roughness value and low hexagonal pits density on the GaN surface must be found

Brassinosteroid signaling-dependent root responses to prolonged elevated ambient temperature

Due to their sessile nature, plants have to cope with and adjust to their fluctuating environment. Temperature elevation stimulates the growth of Arabidopsis aerial parts. This process is mediated by increased biosynthesis of the growth-promoting hormone auxin. How plant roots respond to elevated ambient temperature is however still elusive. Here we present strong evidence that temperature elevation impinges on brassinosteroid hormone signaling to alter root growth. We show that elevated temperature leads to increased root elongation, independently of auxin or factors known to drive temperature-mediated shoot growth. We further demonstrate that brassinosteroid signaling regulates root responses to elevated ambient temperature. Increased growth temperature specifically impacts on the level of the brassinosteroid receptor BRI1 to downregulate brassinosteroid signaling and mediate root elongation. Our results establish that BRI1 integrates temperature and brassinosteroid signaling to regulate root growth upon long-term changes in environmental conditions associated with global warming.Moderate heat stimulates the growth of Arabidopsis shoots in an auxin-dependent manner. Here, Martins et al. show that elevated ambient temperature modifies root growth by reducing the BRI1 brassinosteroid-receptor protein level and downregulating brassinosteroid signaling

Advanced Cataloging of Lysine-63 Polyubiquitin Networks by Genomic, Interactome, and Sensor-based Proteomic Analyses

The lack of resolution on the many different ubiquitin chain types found in eukaryotic cells has been a major hurdle to our understanding of their specific roles. We currently have very little insight into the cellular and physiological functions of lysine(K)63-linked ubiquitin chains, although they are the second most abundant forms of ubiquitin in plant cells. To overcome this, we developed several large-scale approaches aiming at characterizing i) the E2-E3 ubiquitination machinery driving K63-linked ubiquitin chain formation, and ii) K63 polyubiquitination targets to provide the most comprehensive picture of K63 polyubiquitin networks in plants. Our work identified the UBC35/36 E2s as the major driver of K63 polyubiquitin chain formation and highlights the major role of these E2s in plant growth and development. Interactome approaches allowed us to identify many proteins interacting with the K63 polyubiquitination-dedicated UBC35/36 E2s and their cognate E2 variants, including over a dozen of E3s and their putative targets. In parallel, we have improved the in vivo detection of proteins decorated with K63-linked ubiquitin chains by sensor-based proteomics, yielding new insight into K63 polyubiquitination roles in plant cells. Altogether, this work strongly increases our understanding of K63 polyubiquitination networks and functions in plants

A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis

International audienceRhizobia and legumes establish symbiotic interactions leading to the production of root nodules, in which bacteria fix atmospheric nitrogen for the plant's benefit. This symbiosis is efficient because of the high rhizobia population within nodules. Here, we investigated how legumes accommodate such bacterial colonization. We used a reverse genetic approach to identify a Medicago truncatula gene, SymCRK, which encodes a cysteine-rich receptor-like kinase that is required for rhizobia maintenance within the plant cells, and performed detailed phenotypic analyses of the corresponding mutant. The Medicago truncatula symCRK mutant developed nonfunctional and necrotic nodules. A nonarginine asparate (nonRD) motif, typical of receptors involved in innate immunity, is present in the SymCRK kinase domain. Similar to the dnf2 mutant, bacteroid differentiation defect, defense-like reactions and early senescence were observed in the symCRK nodules. However, the dnf2 and symCRK nodules differ by their degree of colonization, which is higher in symCRK. Furthermore, in contrast to dnf2, symCRK is not a conditional mutant. These results suggest that in M. truncatula at least two genes are involved in the symbiotic control of immunity. Furthermore, phenotype differences between the two mutants suggest that two distinct molecular mechanisms control suppression of plant immunity during nodulation