Modeling the organization of the WUSCHEL expression domain in the shoot apical meristem

Motivation: The above-ground tissues of higher plants are generated from a small region of cells situated at the plant apex called the shoot apical meristem. An important genetic control circuit modulating the size of the Arabidopsis thaliana meristem is a feed-back network between the CLAVATA3 and WUSCHEL genes. Although the expression patterns for these genes do not overlap, WUSCHEL activity is both necessary and sufficient (when expressed ectopically) for the induction of CLAVATA3 expression. However, upregulation of CLAVATA3 in conjunction with the receptor kinase CLAVATA1 results in the downregulation of WUSCHEL. Despite much work, experimental data for this network are incomplete and additional hypotheses are needed to explain the spatial locations and dynamics of these expression domains. Predictive mathematical models describing the system should provide a useful tool for investigating and discriminating among possible hypotheses, by determining which hypotheses best explain observed gene expression dynamics. Results: We are developing a method using in vivo live confocal microscopy to capture quantitative gene expression data and create templates for computational models. We present two models accounting for the organization of the WUSCHEL expression domain. Our preferred model uses a reaction-diffusion mechanism in which an activator induces WUSCHEL expression. This model is able to organize the WUSCHEL expression domain. In addition, the model predicts the dynamical reorganization seen in experiments where cells, including the WUSCHEL domain, are ablated, and it also predicts the spatial expansion of the WUSCHEL domain resulting from removal of the CLAVATA3 signal

Nitrate modulates stem cell dynamics in Arabidopsis shoot meristems through cytokinins

The shoot apical meristem (SAM) is responsible for the generation of all the aerial parts of plants. Given its critical role, dynamical changes in SAM activity should play a central role in the adaptation of plant architecture to the environment. Using quantitative microscopy, grafting experiments, and genetic perturbations, we connect the plant environment to the SAM by describing the molecular mechanism by which cytokinins signal the level of nutrient availability to the SAM. We show that a systemic signal of cytokinin precursors mediates the adaptation of SAM size and organogenesis rate to the availability of mineral nutrients by modulating the expression of WUSCHEL, a key regulator of stem cell homeostasis. In time-lapse experiments, we further show that this mechanism allows meristems to adapt to rapid changes in nitrate concentration, and thereby modulate their rate of organ production to the availability of mineral nutrients within a few days. Our work sheds light on the role of the stem cell regulatory network by showing that it not only maintains meristem homeostasis but also allows plants to adapt to rapid changes in the environment

CT scan screening is associated with increased distress among subjects of the APExS

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to assess the psychological consequences of HRCT scan screening in retired asbestos-exposed workers.</p> <p>Methods</p> <p>A HRCT-scan screening program for asbestos-related diseases was carried out in four regions of France. At baseline (T1), subjects filled in self-administered occupational questionnaires. In two of the regions, subjects also received a validated psychological scale, namely the psychological consequences questionnaire (PCQ). The physician was required to provide the subject with the results of the HRCT scan at a final visit. A second assessment of psychological consequences was performed 6 months after the HRCT-scan examination (T2). PCQ scores were compared quantitatively (t-test, general linear model) and qualitatively (chi²-test, logistic regression) to screening results. Multivariate analyses were adjusted for gender, age, smoking, asbestos exposure and counseling.</p> <p>Results</p> <p>Among the 832 subjects included in this psychological impact study, HRCT-scan screening was associated with a significant increase of the psychological score 6 months after the examination relative to baseline values (8.31 to 10.08, p < 0.0001, t-test). This increase concerned patients with an abnormal HRCT-scan result, regardless of the abnormalities, but also patients with normal HRCT-scans after adjustment for age, gender, smoking status, asbestos exposure and counseling visit. The greatest increase was observed for pleural plaques (+3.60; 95%CI [+2.15;+5.06]), which are benign lesions. Detection of isolated pulmonary nodules was also associated with a less marked but nevertheless significant increase of distress (+1.88; 95%CI [+0.34;+3.42]). However, analyses based on logistic regressions only showed a close to significant increase of the proportion of subjects with abnormal PCQ scores at T2 for patients with asbestosis (OR = 1.92; 95%CI [0.97-3.81]) or with two or more diseases (OR = 2.04; 95%CI [0.95-4.37]).</p> <p>Conclusion</p> <p>This study suggests that HRCT-scan screening may be associated with increased distress in asbestos-exposed subjects. If confirmed, these results may have consequences for HRCT-scan screening recommendations.</p

DEP and AFO Regulate Reproductive Habit in Rice

Sexual reproduction is essential for the life cycle of most angiosperms. However, pseudovivipary is an important reproductive strategy in some grasses. In this mode of reproduction, asexual propagules are produced in place of sexual reproductive structures. However, the molecular mechanism of pseudovivipary still remains a mystery. In this work, we found three naturally occurring mutants in rice, namely, phoenix (pho), degenerative palea (dep), and abnormal floral organs (afo). Genetic analysis of them indicated that the stable pseudovivipary mutant pho was a double mutant containing both a Mendelian mutation in DEP and a non-Mendelian mutation in AFO. Further map-based cloning and microarray analysis revealed that dep mutant was caused by a genetic alteration in OsMADS15 while afo was caused by an epigenetic mutation in OsMADS1. Thus, OsMADS1 and OsMADS15 are both required to ensure sexual reproduction in rice and mutations of them lead to the switch of reproductive habit from sexual to asexual in rice. For the first time, our results reveal two regulators for sexual and asexual reproduction modes in flowering plants. In addition, our findings also make it possible to manipulate the reproductive strategy of plants, at least in rice

Observing the cell in its native state: Imaging subcellular dynamics in multicellular organisms

This is the author accepted manuscript. The final version is available from the American Association for the Advancement of Science via the DOI in this recordTrue physiological imaging of subcellular dynamics requires studying cells within their parent organisms, where all the environmental cues that drive gene expression, and hence the phenotypes that we actually observe, are present. A complete understanding also requires volumetric imaging of the cell and its surroundings at high spatiotemporal resolution, without inducing undue stress on either. We combined lattice light-sheet microscopy with adaptive optics to achieve, across large multicellular volumes, noninvasive aberration-free imaging of subcellular processes, including endocytosis, organelle remodeling during mitosis, and the migration of axons, immune cells, and metastatic cancer cells in vivo. The technology reveals the phenotypic diversity within cells across different organisms and developmental stages and may offer insights into how cells harness their intrinsic variability to adapt to different physiological environments.Howard Hughes Medical Institute (HHMI)BiogenIonis PharmaceuticalsNational Institutes of Health (NIH)University of ExeterCarol M. Baldwin FoundationDamon Runyon Cancer Research FoundationNational Science Foundation (NSF)Pew Charitable Trust

Dosage-Sensitive Function of RETINOBLASTOMA RELATED and Convergent Epigenetic Control Are Required during the Arabidopsis Life Cycle

The plant life cycle alternates between two distinct multi-cellular generations, the reduced gametophytes and the dominant sporophyte. Little is known about how generation-specific cell fate, differentiation, and development are controlled by the core regulators of the cell cycle. In Arabidopsis, RETINOBLASTOMA RELATED (RBR), an evolutionarily ancient cell cycle regulator, controls cell proliferation, differentiation, and regulation of a subset of Polycomb Repressive Complex 2 (PRC2) genes and METHYLTRANSFERASE 1 (MET1) in the male and female gametophytes, as well as cell fate establishment in the male gametophyte. Here we demonstrate that RBR is also essential for cell fate determination in the female gametophyte, as revealed by loss of cell-specific marker expression in all the gametophytic cells that lack RBR. Maintenance of genome integrity also requires RBR, because diploid plants heterozygous for rbr (rbr/RBR) produce an abnormal portion of triploid offspring, likely due to gametic genome duplication. While the sporophyte of the diploid mutant plants phenocopied wild type due to the haplosufficiency of RBR, genetic analysis of tetraploid plants triplex for rbr (rbr/rbr/rbr/RBR) revealed that RBR has a dosage-dependent pleiotropic effect on sporophytic development, trichome differentiation, and regulation of PRC2 subunit genes CURLY LEAF (CLF) and VERNALIZATION 2 (VRN2), and MET1 in leaves. There were, however, no obvious cell cycle and cell proliferation defects in these plant tissues, suggesting that a single functional RBR copy in tetraploids is capable of maintaining normal cell division but is not sufficient for distinct differentiation and developmental processes. Conversely, in leaves of mutants in sporophytic PRC2 subunits, trichome differentiation was also affected and expression of RBR and MET1 was reduced, providing evidence for a RBR-PRC2-MET1 regulatory feedback loop involved in sporophyte development. Together, dosage-sensitive RBR function and its genetic interaction with PRC2 genes and MET1 must have been recruited during plant evolution to control distinct generation-specific cell fate, differentiation, and development

Nomad DNA — A model for movement and duplication of DNA sequences in plant genomes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43425/1/11103_2004_Article_BF00019160.pd