SUPPRESSOR OF MAX2 1-LIKE (SMXL) homologs are MAX2-dependent repressors of Physcomitrium patens growth

SUPPRESSOR OF MAX2 (SMAX)1-LIKE (SMXL) proteins are a plant-specific clade of type I HSP100/Clp-ATPases. SMXL genes are present in virtually all land plant genomes. However, they have mainly been studied in angiosperms. In Arabidopsis (Arabidopsis thaliana), 3 functional SMXL subclades have been identified: SMAX1/SMXL2, SMXL345, and SMXL678. Of these, 2 subclades ensure endogenous phytohormone signal transduction. SMAX1/SMXL2 proteins are involved in KAI2 ligand (KL) signaling, while SMXL678 proteins are involved in strigolactone (SL) signaling. Many questions remain regarding the mode of action of these proteins, as well as their ancestral roles. We addressed these questions by investigating the functions of the 4 SMXL genes in the moss Physcomitrium patens. We demonstrate that PpSMXL proteins are involved in the conserved ancestral MAX2-dependent KL signaling pathway and negatively regulate growth. However, PpSMXL proteins expressed in Arabidopsis cannot replace SMAX1 or SMXL2 function in KL signaling, whereas they can functionally replace SMXL4 and SMXL5 and restore root growth. Therefore, the molecular functions of SMXL proteins are conserved, but their interaction networks are not. Moreover, the PpSMXLC/D clade positively regulates SL signal transduction in P. patens. Overall, our data reveal that SMXL proteins in moss mediate crosstalk between the SL and KL signaling pathways.

Synthesis and signalling of strigolactone and KAI2-ligand signals in bryophytes

Strigolactones (SLs), long known as butenolide rhizospheric signals, have been recognized since 2008 as a class of hormones regulating many aspects of plant development. Many authors also anticipate 'KAI2-ligand' (KL) as a novel class of phytohormones; however, this ligand remains elusive. Core genes of SL and KL pathways, first described in angiosperms, are found in all land plants and some even in green algae. This review reports current knowledge of these pathways in bryophytes. Data on the pathways mostly come from two models: the moss Physcomitrium patens and the liverwort Marchantia. Gene targeting methods have allowed functional analyses of both models. Recent work in Marchantia suggests that SLs' ancestral role was to recruit beneficial microbes as arbuscular mycorrhizal fungi. In contrast, the hormonal role of SLs observed in P. patens is probably a result of convergent evolution. Evidence for a functional KL pathway in both bryophyte models is very recent. Nevertheless, many unknowns remain and warrant a more extensive investigation of SL and KL pathways in various land plant lineages.

Expansion of the Strigolactone Profluorescent Probes Repertory: The Right Probe for the Right Application

Strigolactones (SLs) are intriguing phytohormones that not only regulate plant development and architecture but also interact with other organisms in the rhizosphere as root parasitic plants (Striga, Orobanche, and Phelipanche) and arbuscular mycorrhizal fungi. Starting with a pioneering work in 2003 for the isolation and identification of the SL receptor in parasitic weeds, fluorescence labeling of analogs has proven a major strategy to gain knowledge in SL perception and signaling. Here, we present novel chemical tools for understanding the SL perception based on the enzymatic properties of SL receptors. We designed different profluorescent SL Guillaume Clavé (GC) probes and performed structure-activity relationship studies on pea, Arabidopsis thaliana, and Physcomitrium (formerly Physcomitrella) patens. The binding of the GC probes to PsD14/RMS3, AtD14, and OsD14 proteins was tested. We demonstrated that coumarin-based profluorescent probes were highly bioactive and well-adapted to dissect the enzymatic properties of SL receptors in pea and a resorufin profluorescent probe in moss, contrary to the commercially available fluorescein profluorescent probe, Yoshimulactone Green (YLG). These probes offer novel opportunities for the studies of SL in various plants.

Masks Start to Drop: Suppressor of MAX2 1-Like Proteins Reveal Their Many Faces

Although the main players of the strigolactone (SL) signaling pathway have been characterized genetically, how they regulate plant development is still poorly understood. Of central importance are the SUPPRESSOR OF MAX2 1-LIKE (SMXL) proteins that belong to a family of eight members in Arabidopsis thaliana, of which one subclade is involved in SL signaling and another one in the pathway of the chemically related karrikins. Through proteasomal degradation of these SMXLs, triggered by either DWARF14 (D14) or KARRIKIN INSENSITIVE2 (KAI2), several physiological processes are controlled, such as, among others, shoot and root architecture, seed germination, and seedling photomorphogenesis. Yet another clade has been shown to be involved in vascular development, independently of the D14 and KAI2 actions and not relying on proteasomal degradation. Despite their role in several aspects of plant development, the exact molecular mechanisms by which SMXLs regulate them are not completely unraveled. To fill the major knowledge gap in understanding D14 and KAI2 signaling, SMXLs are intensively studied, making it challenging to combine all the insights into a coherent characterization of these important proteins. To this end, this review provides an in-depth exploration of the recent data regarding their physiological function, evolution, structure, and molecular mechanism. In addition, we propose a selection of future perspectives, focusing on the apparent localization of SMXLs in subnuclear speckles, as observed in transient expression assays, which we couple to recent advances in the field of biomolecular condensates and liquid-liquid phase separation.

The Physcomitrium (Physcomitrella) patens PpKAI2L receptors for strigolactones and related compounds function via MAX2-dependent and -independent pathways

In angiosperms, the α/β hydrolase DWARF14 (D14), along with the F-box protein MORE AXILLARY GROWTH2 (MAX2), perceives strigolactones (SL) to regulate developmental processes. The key SL biosynthetic enzyme CAROTENOID CLEAVAGE DIOXYGENASE8 (CCD8) is present in the moss Physcomitrium patens, and PpCCD8-derived compounds regulate moss extension. The PpMAX2 homolog is not involved in the SL response, but 13 PpKAI2LIKE (PpKAI2L) genes homologous to the D14 ancestral paralog KARRIKIN INSENSITIVE2 (KAI2) encode candidate SL receptors. In Arabidopsis thaliana, AtKAI2 perceives karrikins and the elusive endogenous KAI2-Ligand (KL). Here, germination assays of the parasitic plant Phelipanche ramosa suggested that PpCCD8-derived compounds are likely noncanonical SLs. (+)-GR24 SL analog is a good mimic for PpCCD8-derived compounds in P. patens, while the effects of its enantiomer (-)-GR24, a KL mimic in angiosperms, are minimal. Interaction and binding assays of seven PpKAI2L proteins pointed to the stereoselectivity toward (-)-GR24 for a single clade of PpKAI2L (eu-KAI2). Enzyme assays highlighted the peculiar behavior of PpKAI2L-H. Phenotypic characterization of Ppkai2l mutants showed that eu-KAI2 genes are not involved in the perception of PpCCD8-derived compounds but act in a PpMAX2-dependent pathway. In contrast, mutations in PpKAI2L-G, and -J genes abolished the response to the (+)-GR24 enantiomer, suggesting that PpKAI2L-G, and -J proteins are receptors for moss SLs.

Phytohormone biosynthesis and signaling pathways of mosses

Most known phytohormones regulate moss development. We present a comprehensive view of the synthesis and signaling pathways for the most investigated of these compounds in mosses, focusing on the model Physcomitrium patens. The last 50 years of research have shown that most of the known phytohormones are synthesized by the model moss Physcomitrium patens (formerly Physcomitrella patens) and regulate its development, in interaction with responses to biotic and abiotic stresses. Biosynthesis and signaling pathways are best described in P. patens for the three classical hormones auxins, cytokinins and abscisic acid. Furthermore, their roles in almost all steps of development, from early filament growth to gametophore development and sexual reproduction, have been the focus of much research effort over the years. Evidence of hormonal roles exist for ethylene and for CLE signaling peptides, as well as for salicylic acid, although their possible effects on development remain unclear. Production of brassinosteroids by P. patens is still debated, and modes of action for these compounds are even less known. Gibberellin biosynthesis and signaling may have been lost in P. patens, while gibberellin precursors such as ent-kaurene derivatives could be used as signals in a yet to discover pathway. As for jasmonic acid, it is not used per se as a hormone in P. patens, but its precursor OPDA appears to play a corresponding role in defense against abiotic stress. We have tried to gather a comprehensive view of the biosynthesis and signaling pathways for all these compounds in mosses, without forgetting strigolactones, the last class of plant hormones to be reported. Study of the strigolactone response in P. patens points to a novel signaling compound, the KAI2-ligand, which was likely employed as a hormone prior to land plant emergence.

Methods for Medium-Scale Study of Biological Effects of Strigolactone-Like Molecules on the Moss Physcomitrium (Physcomitrella) patens

As a bryophyte and model plant, the moss Physcomitrium (Physcomitrella) patens (P. patens) is particularly well adapted to hormone evolution studies. Gene targeting through homologous recombination or CRISPR-Cas9 system, genome sequencing, and numerous transcriptomic datasets has allowed for molecular genetics studies and much progress in Evo-Devo knowledge. As to strigolactones, like for other hormones, both phenotypical and transcriptional responses can be studied, in both WT and mutant plants. However, as in any plant species, medium- to large-scale phenotype characterization is necessary, owing to the general high phenotypic variability. Therefore, many biological replicates are required. This may translate to large amount of the investigated compounds, particularly expensive (or difficult to synthesize) in the case of strigolactones. These issues prompted us to improve existing methods to limit the use of scarce/expensive compounds, as well as to simplify subsequent measures/sampling of P. patens. We hence scaled up well-tried experiments, in order to increment the number of tested genotypes in one given experiment.In this chapter, we will describe three methods we set up to study the response to strigolactones and related compounds in P. patens.

Design of a comprehensive microfluidic and microscopic toolbox for the ultra-wide spatio-temporal study of plant protoplasts development and physiology

BACKGROUND

Plant protoplasts are basic plant cells units in which the pecto-cellulosic cell wall has been removed, but the plasma membrane is intact. One of the main features of plant cells is their strong plasticity, and their propensity to regenerate an organism from a single cell. Methods and differentiation protocols used in plant physiology and biology usually involve macroscopic vessels and containers that make difficult, for example, to follow the fate of the same protoplast all along its full development cycle, but also to perform continuous studies of the influence of various gradients in this context. These limits have hampered the precise study of regeneration processes.

RESULTS

Herein, we present the design of a comprehensive, physiologically relevant, easy-to-use and low-cost microfluidic and microscopic setup for the monitoring of Physcomitrella patens (P. patens) growth and development on a long-term basis. The experimental solution we developed is made of two parts (i) a microfluidic chip composed of a single layer of about a hundred flow-through microfluidic traps for the immobilization of protoplasts, and (ii) a low-cost, light-controlled, custom-made microscope allowing the continuous recording of the moss development in physiological conditions. We validated the experimental setup with three proofs of concepts: (i) the kinetic monitoring of first division steps and cell wall regeneration, (ii) the influence of the photoperiod on growth of the protonemata, and (iii) finally the induction of leafy buds using a phytohormone, cytokinin.

CONCLUSIONS

We developed the design of a comprehensive, physiologically relevant, easy-to-use and low-cost experimental setup for the study of P. patens development in a microfluidic environment. This setup allows imaging of P. patens development at high resolution and over long time periods.

Physcomitrella patens MAX2 characterization suggests an ancient role for this F-box protein in photomorphogenesis rather than strigolactone signalling

Strigolactones (SLs) are key hormonal regulators of flowering plant development and are widely distributed amongst streptophytes. In Arabidopsis, SLs signal via the F-box protein MORE AXILLARY GROWTH2 (MAX2), affecting multiple aspects of development including shoot branching, root architecture and drought tolerance. Previous characterization of a Physcomitrella patens moss mutant with defective SL synthesis supports an ancient role for SLs in land plants, but the origin and evolution of signalling pathway components are unknown. Here we investigate the function of a moss homologue of MAX2, PpMAX2, and characterize its role in SL signalling pathway evolution by genetic analysis. We report that the moss Ppmax2 mutant shows very distinct phenotypes from the moss SL-deficient mutant. In addition, the Ppmax2 mutant remains sensitive to SLs, showing a clear transcriptional SL response in dark conditions, and the response to red light is also altered. These data suggest divergent evolutionary trajectories for SL signalling pathway evolution in mosses and vascular plants. In P. patens, the primary roles for MAX2 are in photomorphogenesis and moss early development rather than in SL response, which may require other, as yet unidentified, factors.

The Physcomitrella patens gene atlas project: large-scale RNA-seq based expression data

High-throughput RNA sequencing (RNA-seq) has recently become the method of choice to define and analyze transcriptomes. For the model moss Physcomitrella patens, although this method has been used to help analyze specific perturbations, no overall reference dataset has yet been established. In the framework of the Gene Atlas project, the Joint Genome Institute selected P. patens as a flagship genome, opening the way to generate the first comprehensive transcriptome dataset for this moss. The first round of sequencing described here is composed of 99 independent libraries spanning 34 different developmental stages and conditions. Upon dataset quality control and processing through read mapping, 28 509 of the 34 361 v3.3 gene models (83%) were detected to be expressed across the samples. Differentially expressed genes (DEGs) were calculated across the dataset to permit perturbation comparisons between conditions. The analysis of the three most distinct and abundant P. patens growth stages - protonema, gametophore and sporophyte - allowed us to define both general transcriptional patterns and stage-specific transcripts. As an example of variation of physico-chemical growth conditions, we detail here the impact of ammonium supplementation under standard growth conditions on the protonemal transcriptome. Finally, the cooperative nature of this project allowed us to analyze inter-laboratory variation, as 13 different laboratories around the world provided samples. We compare differences in the replication of experiments in a single laboratory and between different laboratories.

Environmental scenarii for the degradation of oxo-polymers

The fate of oxo-polymers in nature is strongly dependent on environmental conditions, mainly on the intensity and duration of sunshine, which vary with the season and the climate. In this work, we report the effect of different scenarii on the production and the molecular composition of oligomers released from oxo-biodegradable HDPE films. Under our experimental conditions, the duration of accelerated weathering corresponded to a period of 3 months to 3 years of exposure to outside conditions under temperate climate. In addition, the oligomers were extracted in three different solvents: i) water to mimics the natural environment; ii) acetone and chloroform to identify oligomers trapped in the polymer matrix. The combination of high-resolution mass spectrometry and ¹H NMR spectroscopy gives an extensive picture of the relative concentrations and the structural compositions of the extracted oligomers in the different tested conditions. In particular, the masses, the number of oxygen and carbon atoms could be determined for up to 2283 molecules. Globally the concentration and the size of oligomers increased with the duration of extraction, the level of aging of the polymer and the use of non-polar solvents. Surprisingly, the presence of highly oxidized molecules in acetone and chloroform extract, suggested an important swelling of HPDE films in these solvents and a better diffusion of these oligomers in the matrix. In nature, the biodegradability of oligomers could result from processes occurring both at the molecular (oxidation) and the macromolecular (diffusion and release) levels.

Characterization of oxidized oligomers from polyethylene films by mass spectrometry and NMR spectroscopy before and after biodegradation by a Rhodococcus rhodochrous strain

The objective of this work was to develop a new approach to assess the specificity and the efficiency of biodegradation of oxidized oligomers extracted from aged HDPE polyethylene films and to bring insight on the mechanisms occurring during biodegradation. ¹H NMR spectroscopy and LC Orbitrap™ mass spectrometry were combined together with data processing using Kendrick mass defect calculation and Van Krevelen Diagram. We showed that the molecular weight of extracted oligomers was lower than 850 Da with maximum chain length of 55 carbon atoms. The oligomers were divided into 11 classes of molecules with different oxidation state ranging from 0 to 10. All classes included series of chemically related compounds including up to 19 molecules. 95% of the soluble oligomers were assimilated by a strain of Rhodococcus rhodocchrous after 240 days of incubation. Large highly oxidized molecules completely disappeared while the other classes of molecules were still represented. Molecules containing 0-1 oxygen atom were less degraded. A strong shift to smaller molecules (<450 Da, 25 carbon atoms) was observed suggesting that longer molecules disappeared more rapidly than the smaller ones. It opens new perspectives on biodegradation processes as not only intracellular β-oxidation must be considered but also extracellular mechanisms leading to chain cleavages.

An histidine covalent receptor and butenolide complex mediates strigolactone perception

Strigolactone plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. They contain an ABC tricyclic lactone connected to a butenolide group, the D ring. The DWARF14 (D14) strigolactone receptor belongs to the superfamily of α/β-hydrolases, and is known to hydrolyze the bond between the ABC lactone and the D ring. Here we characterized the binding and catalytic functions of RAMOSUS3 (RMS3), the pea (Pisum sativum) ortholog of rice (Oryza sativa) D14 strigolactone receptor. Using new profluorescent probes with strigolactone-like bioactivity, we found that RMS3 acts as a single-turnover enzyme that explains its apparent low enzymatic rate. We demonstrated the formation of a covalent RMS3-D-ring complex, essential for bioactivity, in which the D ring was attached to histidine 247 of the catalytic triad. These results reveal an undescribed mechanism of plant hormone reception in which the receptor performs an irreversible enzymatic reaction to generate its own ligand.

[Interest of punch skin grafting for the treatment of painful ulcers]

INTRODUCTION

Skin leg ulcers are chronic painful wounds. The treatment of these ulcers is crucial for patients because pain has a significant impact on their daily lives. The analgesic effect of punch skin grafting (PSG) for the treatment of painful ulcers is not well described. The objective of the study is to assess the level of pain in patients with an ulcerated wound and to see if there is an analgesic effect of PSG.

PATIENT AND METHODS

It was a single-center, non-interventional study conducted in hospitalized patients with one or several ulcer(s) of any type and which has been painful for more than six weeks. Pain was assessed before, the day after a PSG and then on the way out of hospital by a questionnaire and a numeric pain rating scale. Permanent pain and pain peaks were identified.

RESULTS

Forty one patients were included (23 men and 18 women) with mean age of 73±21 years, 36% (n=15) with arterial ulcers, 36% (n=15) with venous ulcers, 12% (n=5) with necrotic angiodermatitis, 12% (n=5) with mixed ulcers and 4% (n=2) with "other ulcers" (due to infection and use of Hydroxycarbamide). On day 1 of PSG, patients showed an improvement in terms of permanent pain (77%, n=24/31) and pain peaks (90%, n=37/41) respectively and 90% (n=28/31) and 95% (n=39/41) on the last day at hospital. Reduction in the use of strong opioids was found in 13 patients (81%).

CONCLUSION

Punch skin grafting is a simple and validated treatment, which can reduce or eliminate pain related to ulcers. It has an effect on permanent pain and pain peaks. Its efficacy is particularly demonstrated on venous ulcers and mixed ulcers but also initially painful ulcers such as necrotic angiodermatitis or arterial ulcers.

Structural modelling and transcriptional responses highlight a clade of PpKAI2-LIKE genes as candidate receptors for strigolactones in Physcomitrella patens

A set of PpKAI2 - LIKE paralogs that may encode strigolactone receptors in Physcomitrella patens were identified through evolutionary, structural, and transcriptional analyses, suggesting that strigolactone perception may have evolved independently in basal land plants in a similar manner as spermatophytes. Carotenoid-derived compounds known as strigolactones are a new class of plant hormones that modulate development and interactions with parasitic plants and arbuscular mycorrhizal fungi. The strigolactone receptor protein DWARF14 (D14) belongs to the α/β hydrolase family. D14 is closely related to KARRIKIN INSENSITIVE2 (KAI2), a receptor of smoke-derived germination stimulants called karrikins. Strigolactone and karrikin structures share a butenolide ring that is necessary for bioactivity. Charophyte algae and basal land plants produce strigolactones that influence their development. However phylogenetic studies suggest that D14 is absent from algae, moss, and liverwort genomes, raising the question of how these basal plants perceive strigolactones. Strigolactone perception during seed germination putatively evolved in parasitic plants through gene duplication and neofunctionalization of KAI2 paralogs. The moss Physcomitrella patens shows an increase in KAI2 gene copy number, similar to parasitic plants. In this study we investigated whether P. patens KAI2-LIKE (PpKAI2L) genes may contribute to strigolactone perception. Based on phylogenetic analyses and homology modelling, we predict that a clade of PpKAI2L proteins have enlarged ligand-binding cavities, similar to D14. We observed that some PpKAI2L genes have transcriptional responses to the synthetic strigolactone GR24 racemate or its enantiomers. These responses were influenced by light and dark conditions. Moreover, (+)-GR24 seems to be the active enantiomer that induces the transcriptional responses of PpKAI2L genes. We hypothesize that members of specific PpKAI2L clades are candidate strigolactone receptors in moss.

Strigolactone biosynthesis and signaling in plant development

Strigolactones (SLs), first identified for their role in parasitic and symbiotic interactions in the rhizosphere, constitute the most recently discovered group of plant hormones. They are best known for their role in shoot branching but, more recently, roles for SLs in other aspects of plant development have emerged. In the last five years, insights into the SL biosynthetic pathway have also been revealed and several key components of the SL signaling pathway have been identified. Here, and in the accompanying poster, we summarize our current understanding of the SL pathway and discuss how this pathway regulates plant development.

[Leg ulcers: Should general practitioners hospitalize their patients?]

OBJECTIVES

Determine whether general practitioners have sufficient expertise in the field of leg ulcers.

METHOD

A cross-sectional survey was conducted among 179 general practitioners working in the region Île-de-France to evaluate the implementation of leg ulcer guidelines issued by the Superior Health Authority (HAS) in 2006. Participating physicians were either internship supervisors or practitioners in Paris' 14th district.

RESULTS

The first hundred usable answers (response rate 65%) came from 71 internship supervisors and 29 practitioners of Paris' 14th district. Only 40% of the physicians were aware of the guidelines, with no significant difference noted between the two groups. 9/10 practitioners examined less than 10 patients with leg ulcers per year. Physical examinations were done according to the guidelines and a venous Doppler was prescribed in two thirds of the cases. The ankle-brachial pressure index (ABPI) essential to diagnose lower limb arteriopathy was measured for only 10% of the patients. In accordance with the guidelines, compression was by far (73%) considered as the main treatment as compared to dressing (37%), but compression therapy was well prescribed in only one-third of the cases. Despite poor prognosis criteria (characteristic and time course), referral for a specialized opinion was rare.

CONCLUSION

Even if they were not always aware of the detailed guidelines, the practitioners applied the main recommendations. Nevertheless, practices could be improved by measuring the ABPI, searching for a diagnosis of arteriopathy, and better prescription of compression therapy. General practitioners should refer patients with leg ulcers to a specialized hospital unit.

[Vascular myeloproliferative neoplasm with normal cell blood count: Exploration and medical management]

Negative BCR ABL myeloproliferative neoplasm (MPN) such as polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (MFP) are clonal hematological malignancies and may lead to a high risk of venous, arterial or microcirculatory thrombosis. Atypical sites of thrombosis can sometimes reveal the neoplasm disorder. Their diagnoses are a major issue because of the propensity to develop acute myeloid leukemia and/or myelofibrosis. The acquired JAK2V617F variant (Janus kinase 2; 9p24) is a prevalent MPN and also a sensitive marker for PV diagnosis (95% positive mutation), but not specific since found in approximately 50% of patients with ET and MFP.

PATIENT AND METHODS

We present a diagnostic and a therapeutic approach based on one patient with microcirculatory ischemic manifestations in the toes, and who had strictly normal cell blood counts and was positive for JAK2V617F mutation: thrombotic risk factor evaluation; bone marrow biopsy; red cell adhesion assays. These experimental assays are promising for the development of new therapeutics in MPN; they assess red cell adherence to the vascular endothelium after the phosphorylation of Lu/BCAM subsequent to a positive JAK2V617F mutation.

RESULTS

Compared with controls, our patient exhibited increased Lu/BCAM receptor phosphorylation and red blood cell adhesion.

CONCLUSION

This development may lead to improved care for patients with thrombotic manifestations, normal blood cell counts, and a positive JAK2V617F mutation: multidisciplinary management, including regular hematological monitoring, could lead to the introduction of a cytoreductive treatment.

Strigolactones inhibit caulonema elongation and cell division in the moss Physcomitrella patens

In vascular plants, strigolactones (SLs) are known for their hormonal role and for their role as signal molecules in the rhizosphere. SLs are also produced by the moss Physcomitrella patens, in which they act as signaling factors for controlling filament extension and possibly interaction with neighboring individuals. To gain a better understanding of SL action at the cellular level, we investigated the effect of exogenously added molecules (SLs or analogs) in moss growth media. We used the previously characterized Ppccd8 mutant that is deficient in SL synthesis and showed that SLs affect moss protonema extension by reducing caulonema cell elongation and mainly cell division rate, both in light and dark conditions. Based on this effect, we set up bioassays to examine chemical structure requirements for SL activity in moss. The results suggest that compounds GR24, GR5, and 5-deoxystrigol are active in moss (as in pea), while other analogs that are highly active in the control of pea branching show little activity in moss. Interestingly, the karrikinolide KAR1, which shares molecular features with SLs, did not have any effect on filament growth, even though the moss genome contains several genes homologous to KAI2 (encoding the KAR1 receptor) and no canonical homologue to D14 (encoding the SL receptor). Further studies should investigate whether SL signaling pathways have been conserved during land plant evolution.

Functional redundancy and/or ongoing pseudogenization among F-box protein genes expressed in Arabidopsis male gametophyte

F-box protein genes family is one of the largest gene families in plants, with almost 700 predicted genes in the model plant Arabidopsis. F-box proteins are key components of the ubiquitin proteasome system that allows targeted protein degradation. Transcriptome analyses indicate that half of these F-box protein genes are found expressed in microspore and/or pollen, i.e., during male gametogenesis. To assess the role of F-box protein genes during this crucial developmental step, we selected 34 F-box protein genes recorded as highly and specifically expressed in pollen and isolated corresponding insertion mutants. We checked the expression level of each selected gene by RT-PCR and confirmed pollen expression for 25 genes, but specific expression for only 10 of the 34 F-box protein genes. In addition, we tested the expression level of selected F-box protein genes in 24 mutant lines and showed that 11 of them were null mutants. Transmission analysis of the mutations to the progeny showed that none of the single mutations was gametophytic lethal. These unaffected transmission efficiencies suggested leaky mutations or functional redundancy among F-box protein genes. Cytological observation of the gametophytes in the mutants confirmed these results. Combinations of mutations in F-box protein genes from the same subfamily did not lead to transmission defect either, further highlighting functional redundancy and/or a high proportion of pseudogenes among these F-box protein genes.

Novel insights into strigolactone distribution and signalling

Strigolactones (SLs), a group of small carotenoid-derived molecules, were first known for their function in the rhizosphere in both symbiotic and parasitic interactions. Most of the progress for deciphering SL biosynthesis and signalling pathways comes from the use of high branching mutants identified in several species demonstrating that SLs also play a hormonal role in plant development. How SLs are perceived by the different organisms on which they show bioactivity is a current major challenge for the growing SL research community. These molecules very likely predate the colonization of land by plants and represent a fascinating example of signalling molecules involved in key innovations during plant evolution.

Functional characterization of the plant ubiquitin regulatory X (UBX) domain-containing protein AtPUX7 in Arabidopsis thaliana

p97/CDC48 is a major AAA-ATPase that acts in many cellular events such as ubiquitin-dependent degradation and membrane fusion. Its specificity depends on a set of adaptor proteins, most of them containing the ubiquitin regulatory X (UBX) domain. Using a differential hybridization system, we isolated a UBX-containing protein that is expressed during the early phase of male gametophyte development in the crop Brassica napus and isolated and characterized its closest Arabidopsis thaliana homolog, AtPUX7. The AtPUX7 gene is expressed broadly in both the sporophyte and gametophyte due to regulation inferred by its first intron. The subcellular localization of AtPUX7 was assigned mainly to the nucleus in both the sporophyte and in pollen, mirroring the AAA-ATPase AtCDC48A localization. Furthermore, AtPUX7 interacts specifically with AtCDC48A in yeast as well as in planta in the nucleus. This interaction was mediated through the AtPUX7 UBX domain, which is located at the protein C-terminus, while an N-terminal UBA domain mediated its interaction with ubiquitin. Consistent with those results, a yeast-three hybrid analysis showed that AtPUX7 can act as a bridge between AtCDC48A and ubiquitin, suggesting a role in targeted protein degradation. It is likely that AtPUX7 acts redundantly with other members of the Arabidopsis PUX family because a null Atpux7-1 mutant does not display obvious developmental defects.

Usefulness of Physcomitrella patens for studying plant organogenesis

In this chapter, we review the main organogenesis features and associated regulation processes of the moss Physcomitrella patens (P. patens), the model plant for the Bryophytes. We highlight how the study of this descendant of the earliest plant species that colonized earth, brings useful keys to understand the mechanisms that determine and control both vascular and non vascular plants organogenesis. Despite its simple morphogenesis pattern, P. patens still requires the fine tuning of organogenesis regulators, including hormone signalling, common to the whole plant kingdom, and which study is facilitated by a high number of molecular tools, among which the powerful possibility of gene targeting/replacement. The recent discovery of moss cells reprogramming capacity completes the picture of an excellent model for studying plant organogenesis.

A SNP associated with alternative splicing of RPT5b causes unequal redundancy between RPT5a and RPT5b among Arabidopsis thaliana natural variation

BACKGROUND

The proteasome subunit RPT5, which is essential for gametophyte development, is encoded by two genes in Arabidopsis thaliana; RPT5a and RPT5b. We showed previously that RPT5a and RPT5b are fully redundant in the Columbia (Col-0) accession, whereas in the Wassilewskia accession (Ws-4), RPT5b does not complement the effect of a strong rpt5a mutation in the male gametophyte, and only partially complements rpt5a mutation in the sporophyte. RPT5bCol-0 and RPT5bWs-4 differ by only two SNPs, one located in the promoter and the other in the seventh intron of the gene.

RESULTS

By exploiting natural variation at RPT5b we determined that the SNP located in RPT5b intron seven, rather than the promoter SNP, is the sole basis of this lack of redundancy. In Ws-4 this SNP is predicted to create a new splicing branchpoint sequence that induces a partial mis-splicing of the pre-mRNA, leading to the introduction of a Premature Termination Codon. We characterized 5 accessions carrying this A-to-T substitution in intron seven and observed a complete correlation between this SNP and both a 10 to 20% level of the RPT5b pre-mRNA mis-splicing and the lack of ability to complement an rpt5a mutant phenotype.

CONCLUSION

The accession-dependent unequal redundancy between RPT5a and RPT5b genes illustrates an example of evolutionary drifting between duplicated genes through alternative splicing.

Thrombolysis of occluded infra-inguinal bypass grafts: is it worthwhile?

BACKGROUND

Thrombosis of an infra-inguinal bypass graft often results in a limb-threatening ischemia. There is no consensus on the optimal management strategy.

AIM OF THE STUDY

To analyse safety and efficacy of catheter-guided intra-arterial thrombolysis to re-open thrombosed infra-inguinal bypass grafts and to identify factors that influence graft patency and limb salvage rate after thrombolytic procedures.

METHODS

A continuous cohort-study of 106 thrombolytic procedures between 1993 to 2008.

RESULTS

Despite a high initial success rate (76%), the mid-term results are less convincing, with a 58% re-occlusion rate at 45 months follow-up. Thrombosed vein grafts, old (2 weeks or more) occlusions, poor run-off and failure to identify or rectify an underlying causative stenosis are determinant for a poor long-term outcome of thrombolytic procedures.

COMMENTS

The outcome results of author's experience are consistent with literature reports. Thrombolysis of occluded infra-inguinal bypass grafts should be limited to selective cases (recent occlusion, prosthetic or vein graft in place since 1 year or more, critical limb ischemia). Despite its obvious advantages, the long-term outcome of thrombolytic procedures is deceiving. The inherent risk of hemorrhagic complications should also be taken in account at the decision making of treatment strategy. The question whether, in general, catheter-guided selective intra-arterial thrombolysis offers a significant advantage over operative revascularisation (thrombectomy or new bypass) remains unanswered. A more selective approach seems to favour thrombolysis as most appropriate strategy in the management of recent (< 2 weeks) thromboses of grafts in place since at least 1 year.

The Arabidopsis proteasome RPT5 subunits are essential for gametophyte development and show accession-dependent redundancy

We investigated the role of the ubiquitin proteasome system (UPS), which allows proteins to be selectively degraded, during gametophyte development in Arabidopsis thaliana. Three mutant alleles altering the UPS were isolated in the Wassilewskija (Ws) accession: they affect the Regulatory Particle 5a (RPT5a) gene, which (along with RPT5b) encodes one of the six AAA-ATPases of the proteasome regulatory particle. In the heterozygous state, all three mutant alleles displayed 50% pollen lethality, suggesting that RPT5a is essential for male gametophyte development. However, a fourth mutant in the Columbia (Col) accession did not display such a phenotype because the RPT5b Col allele complements the rpt5a defect in the male gametophyte, whereas the RPT5b Ws allele does not. Double rpt5a rpt5b mutants showed a complete male and female gametophyte lethal phenotype in a Col background, indicating that RPT5 subunits are essential for both gametophytic phases. Mitotic divisions were affected in double mutant gametophytes correlating with an absence of the proteasome-dependent cyclinA3 degradation. Finally, we show that RPT5b expression is highly increased when proteasome functioning is defective, allowing complementation of the rpt5a mutation. In conclusion, RPT5 subunits are not only essential for both male and female gametophyte development but also display accession-dependent redundancy and are crucial in cell cycle progression.

The POK/AtVPS52 protein localizes to several distinct post-Golgi compartments in sporophytic and gametophytic cells

The organization and dynamics of the plant endomembrane system require both universal and plant-specific molecules and compartments. The latter, despite the growing wealth of information, remains poorly understood. From the study of an Arabidopsis thaliana male gametophytic mutant, it was possible to isolate a gene named POKY POLLEN TUBE (POK) essential for pollen tube tip growth. The similarity between the predicted POK protein sequence and yeast Vps52p, a subunit from the GARP/VFT complex which is involved in the docking of vesicles from the prevacuolar compartment to the Golgi apparatus, suggested that the POK protein plays a role in plant membrane trafficking. Genetic analysis of Arabidopsis mutants affecting AtVPS53 or AtVPS54 genes which encode putative POK partners shows a transmission defect through the male gametophyte for all lines, which is similar to the pok mutant. Using a combination of biochemical approaches and specific antiserum it has been demonstrated that the POK protein is present in phylogenetically divergent plant species, associated with membranes and belongs to a high molecular weight complex. Combination of immunolocalization studies and pharmacological approaches in different plant cells revealed that the POK protein associates with Golgi and post-Golgi compartments. The role of POK in post-Golgi endomembrane trafficking and as a member of a putative plant GARP/VFT complex is discussed.

[Upper limb lymphedema revealing breast cancer]

INTRODUCTION

Upper limb lymphedema occurs in 15 to 20% of patients after breast cancer treatment. Upper limb lymphedema without any history of neoplasia is an unusual situation. In this situation, breast cancer should be suspected.

EXEGESIS

We reported two women, 53 and 67 years old, who developed upper limb lymphedema, 18 and 8 months before the diagnosis of breast cancer. In the two cases, clinical examination (breast and axillary palpation) was normal. In one case, mammography led to the diagnosis and in the other breast MRI was required to confirm the cancer.

DISCUSSION

Upper limb lymphedema may be the presenting clinical feature of breast cancer. Breast cancer should be actively sought despite normal clinical and radiological findings. Breast MRI is required in this situation.

The putative Arabidopsis homolog of yeast vps52p is required for pollen tube elongation, localizes to Golgi, and might be involved in vesicle trafficking

The screening of the Versailles collection of Arabidopsis T-DNA transformants allowed us to identify several male gametophytic mutants, including poky pollen tube (pok). The pok mutant, which could only be isolated as a hemizygous line, exhibits very short pollen tubes, explaining the male-specific transmission defect observed in this line. We show that the POK gene is duplicated in the Arabidopsis genome and that the predicted POK protein sequence is highly conserved from lower to higher eukaryotes. The putative POK homolog in yeast (Saccharomyces cerevisiae), referred to as Vps52p/SAC2, has been shown to be located at the late Golgi and to function in a complex with other proteins, Vps53p, Vps54p, and Vps51p. This complex is involved in retrograde trafficking of vesicles between the early endosomal compartment and the trans-Golgi network. We present the expression patterns of the POK gene and its duplicate P2 in Arabidopsis, and of the putative Arabidopsis homologs of VPS53 and VPS54 of yeast. We show that a POK::GFP fusion protein localizes to Golgi in plant cells, supporting the possibility of a conserved function for Vps52p and POK proteins. These results, together with the expression pattern of the POK::GUS fusion and the lack of plants homozygous for the pok mutation, suggest a more general role for POK in polar growth beyond the pollen tube elongation process.

KINKY POLLEN encodes a SABRE-like protein required for tip growth in Arabidopsis and conserved among eukaryotes

In higher plants, pollen tubes and root hairs share an ancient growth process named tip growth. We have isolated three allelic Arabidopsis mutant lines showing kinky-shaped pollen tubes and, when homozygous, showing shorter and thicker root hairs. The ultrastructure of pollen tubes in these kinky pollen (kip) mutants is similar to that of the wild type; however, time-lapse studies suggest that aberrant pollen tube shape is caused by periodic growth arrests alternated with phases of tube axis reorientation. The KIP gene encodes a protein of 2587 amino acids that is predicted to be targeted to the secretory pathway. KIP mRNA was detected in all organs investigated but was most abundant in pollen and roots. KIP has putative homologues in many eukaryotes, including mammals and yeast, and is similar to the Arabidopsis SABRE gene, whose mutation causes a dwarf phenotype. The phenotype of the kip/sab double mutant suggests related functions for both genes, however, the KIP protein is mostly required for tip-growth.

Five gametophytic mutations affecting pollen development and pollen tube growth in Arabidopsis thaliana

Mutant analysis represents one of the most reliable approaches to identifying genes involved in plant development. The screening of the Versailles collection of Arabidopsis thaliana T-DNA insertion transformants has allowed us to isolate different mutations affecting male gametophytic functions and viability. Among several mutated lines, five have been extensively studied at the genetic, molecular, and cytological levels. For each mutant, several generations of selfing and outcrossing have been carried out, leading to the conclusion that all these mutations are tagged and affect only the male gametophyte. However, only one out of the five mutations is completely penetrant. A variable number of T-DNA copies has integrated in the mutant lines, although all segregate at one mutated locus. Two mutants could be defined as "early mutants": the mutated genes are presumably expressed during pollen grain maturation and their alteration leads to the production of nonfunctional pollen grains. Two other mutants could be defined as "late mutant" since their pollen is able to germinate but pollen tube growth is highly disturbed. Screening for segregation ratio distortions followed by thorough genetic analysis proved to be a powerful tool for identifying gametophytic mutations of all phases of pollen development.

Working together toward the issue of conjugal violence: the work of an interdisciplinary task force

In 1995 each of the Professional Councils at the Royal Victoria Hospital endorsed the creation of an Interdisciplinary Task Force on Conjugal Violence. Task force members were drawn from Medicine, Nursing and Social Work. The overall goal was to increase the quality of care that the interdisciplinary team could provide to their patients. This mandate encompassed three major tasks. First, to study the extent of awareness about the issue among health care professionals; second, to assess their needs for resources and education; and finally, to recommend and implement means of increasing the level of awareness of this health concern among professionals and patients. The task force members educated themselves about conjugal violence and developed a questionnaire that was distributed to health care professionals within the hospital. The number of individuals from each discipline who received the survey was proportionate to their actual number in the center and selected at random. Results of the survey indicated that all groups desired more information and education about the scope of the problem as well as means for assessing and intervening with patients who are abused. The task force developed a Conjugal Abuse Information Package, an Abuse Assessment Screen, a Public Awareness Program and an Ongoing Teaching Program for Health Care Professionals. This project provides an example of how an interdisciplinary health care team can successfully work together for the benefit of patients.

T-DNA mediated disruption of essential gametophytic genes in Arabidopsis is unexpectedly rare and cannot be inferred from segregation distortion alone

Many genes are thought to be expressed during the haploid phase in plants, however, very few haploid-specific genes have been isolated so far. T-DNA insertion mutagenesis is a powerful tool for generating mutations that affect gametophyte viability and function, as disruption of a gene essential for these processes should lead to a defect in the transmission of the gametes. Mutants can therefore be screened on the basis of segregation distortion for a reporter resistance gene contained in the T-DNA. We have screened the Versailles collection of Arabidopsis transformants for 1:1 KanR:KanS segregation after selfing, focussing on gametophyte mutations which show normal transmission through one gametophyte and cause lethality or dysfunction of the other. Only 1.3% (207) of the 16,000 lines screened were scored as good candidates. Thorough genetic analysis of 38 putative T-DNA transmission defect lines (Ttd) identified 8 defective gametophyte mutants, which all showed 0 to 1% T-DNA transmission through the pollen. During the screen, we observed a high background of low-penetrance mutations, often affecting the function of both gametophytes, and many lines which were likely to carry chromosomal rearrangements. The reasons for the small number of retained lines (all male gametophytic) are discussed, as well as the finding that, for most of them, residual T-DNA transmission is obtained through the affected gametophyte.

Telephone follow-up of gynecology day surgery patients. On line for quality and continuity of care

Traditionally, patients who received minor gynecology surgery remained in the hospital for a few days, during which time post-operative care was given by nurses. However, since patients are now often discharged the same day, the responsibility for this care has been transferred to the patients and their families. Because the nursing staff of the Gynecology Day Surgery Unit at the Royal Victoria Hospital believes there is a need for patient-monitoring after discharge and CLSCs do not offer services for this generally healthy clientele, they developed, with the head nurse and the assistant head nurse, a post-operative telephone follow-up program. This idea stemmed from the general need to adapt care as a result of the increase in day surgery. In addition to extending care beyond the hospital walls and improving its quality, this program has increased the job satisfaction of the nurses involved.

Ogura cytoplasmic male-sterility (CMS)-associated orf138 is translated into a mitochondrial membrane polypeptide in male-sterile Brassica cybrids

Transcription of a putative mitochondrial gene (orf138) has previously been correlated with Ogura cytoplasmic male-sterility (CMS) in rapeseed cybrids. In this paper, studies performed on a Brassica cybrid with a different organization of the orf138 locus confirm this association. We also show that mitochondria isolated from male-sterile rapeseed plants synthesize a polypeptide of 19 kDa, which is absent in fertile revertants. Antibodies against a glutathione S-transferase-ORF138 fusion protein were raised to establish that this 19 kDa polypeptide is the product of orf138. The anti-ORF138 serum was used to demonstrate that the orf138 translation product occurs only in sterile cybrids and co-purifies with the mitochondrial membrane fraction.

Sequence and transcript analysis of the Nco2.5 Ogura-specific fragment correlated with cytoplasmic male sterility in Brassica cybrids

Sequence analysis of the Ogura-specific mitochondrial DNA (mtDNA) fragment isolated previously from Brassica cybrids carrying Ogura cytoplasmic male sterility (cms) revealed a tRNA(fMet) sequence, a putative 138 amino acid open reading frame (orf138), and a 158 amino acid ORF (orf158) previously observed in mitochondrial genomes from several other plant species. Transcription mapping showed that both ORFs are present on a 1.4 kb cms-specific transcript. The orf158 sequence is also transcribed in fertile plants on a different mRNA, and thus is unlikely to be related to cms. On the other hand, fertile revertant plants lack transcripts of the orf138 sequence, whose possible role in the mechanism of Ogura cms is discussed.