Sugars promote lateral root formation at low levels but become inhibitory at high C/N or C/P ratios. How sugars suppress lateral root formation is unclear, however. Here we report that WOX7, a member ...of the WUSCHEL related homeobox （WOX） family transcription factors, inhibits lateral root development in a sugar-dependent manner. The number of lateral root primordia increased in wox7 mutants but decreased in plants over-expressing WOX7o Plants expressing the WOX7-VP16 fusion protein produced even more lateral roots than wox7, suggesting that WOX7 acts as a transcriptional repressor in lateral root develop- ment. WOX7 is expressed at all stages of lateral root development, but it is primarily involved in lateral root initiation. Consistent with this, the wox7 mutant had a higher mitotic activity only at early stages of lateral root development. Further studies suggest that WOX7 regulates lateral root development through direct repression of cell cycle genes, particularly CYCD6;1. WOX7 expression was enhanced by sugar, reduced by auxin, but did not respond to salt and mannitoh In the wox7 mutant, the effect of sugar on lateral root formation was mitigated. These results together suggest that WOX7 plays an important role in coupling the lateral root development program and sugar status in plants.
Bundle sheath (BS) cells form a single cell layer surrounding the vascular tissue in leaves. In C3 plants, photosynthesis occurs in both the BS and mesophyll cells, but the BS cells are the major ...sites of photosynthesis in C4 plants, whereas the mesophyll cells are only involved in CO₂ fixation. Because C4 plants are more efficient photosynthetically, introduction of the C4 mechanism into C3 plants is considered a key strategy to improve crop yield. One prerequisite for such C3‐to‐C4 engineering is the ability to manipulate the number and physiology of the BS cells, but the molecular basis of BS cell‐fate specification remains unclear. Here we report that mutations in three GRAS family transcription factors, SHORT‐ROOT (SHR), SCARECROW (SCR) and SCARECROW‐LIKE 23 (SCL23), affect BS cell fate in Arabidopsis thaliana. SCR and SCL23 are expressed specifically in the BS cells and act redundantly in BS cell‐fate specification, but their expression pattern and function diverge at later stages of leaf development. Using ChIP–chip experiments and sugar assays, we show that SCR is primarily involved in sugar transport whereas SCL23 functions in mineral transport. SHR is also essential for BS cell‐fate specification, but it is expressed in the central vascular tissue. However, the SHR protein moves into the BS cells, where it directly regulates SCR and SCL23 expression. SHR, SCR and SCL23 homologs are present in many plant species, suggesting that this developmental pathway for BS cell‐fate specification is likely to be evolutionarily conserved.
The ability to nondestructively image and automatically phenotype complex root systems, like those of rice (Oryza sativa), is fundamental to identifying genes underlying root system architecture ...(RSA). Although root systems are central to plant fitness, identifying genes responsible for RSA remains an underexplored opportunity for crop improvement. Here we describe a nondestructive imaging and analysis system for automated phenotyping and trait ranking of RSA. Using this system, we image rice roots from 12 genotypes. We automatically estimate RSA traits previously identified as important to plant function. In addition, we expand the suite of features examined for RSA to include traits that more comprehensively describe monocot RSA but that are difficult to measure with traditional methods. Using 16 automatically acquired phenotypic traits for 2,297 images from 118 individuals, we observe (1) wide variation in phenotypes among the genotypes surveyed; and (2) greater intergenotype variance of RSA features than variance within a genotype. RSA trait values are integrated into a computational pipeline that utilizes supervised learning methods to determine which traits best separate two genotypes, and then ranks the traits according to their contribution to each pairwise comparison. This trait-ranking step identifies candidate traits for subsequent quantitative trait loci analysis and demonstrates that depth and average radius are key contributors to differences in rice RSA within our set of genotypes. Our results suggest a strong genetic component underlying rice RSA. This work enables the automatic phenotyping of RSA of individuals within mapping populations, providing an integrative framework for quantitative trait loci analysis of RSA.
Ionizing radiation represents the most effective therapy for glioblastoma (World Health Organization grade IV glioma), one of the most lethal human malignancies, but radiotherapy remains only ...palliative because of radioresistance. The mechanisms underlying tumour radioresistance have remained elusive. Here we show that cancer stem cells contribute to glioma radioresistance through preferential activation of the DNA damage checkpoint response and an increase in DNA repair capacity. The fraction of tumour cells expressing CD133 (Prominin-1), a marker for both neural stem cells and brain cancer stem cells, is enriched after radiation in gliomas. In both cell culture and the brains of immunocompromised mice, CD133-expressing glioma cells survive ionizing radiation in increased proportions relative to most tumour cells, which lack CD133. CD133-expressing tumour cells isolated from both human glioma xenografts and primary patient glioblastoma specimens preferentially activate the DNA damage checkpoint in response to radiation, and repair radiation-induced DNA damage more effectively than CD133-negative tumour cells. In addition, the radioresistance of CD133-positive glioma stem cells can be reversed with a specific inhibitor of the Chk1 and Chk2 checkpoint kinases. Our results suggest that CD133-positive tumour cells represent the cellular population that confers glioma radioresistance and could be the source of tumour recurrence after radiation. Targeting DNA damage checkpoint response in cancer stem cells may overcome this radioresistance and provide a therapeutic model for malignant brain cancers.
Long-range interactions between promoters and cis-regulatory elements, such as enhancers, play critical roles in gene regulation. However, the role of three-dimensional (3D) chromatin structure in ...orchestrating changes in transcriptional regulation during direct cell reprogramming is not fully understood.
Here, we performed integrated analyses of chromosomal architecture, epigenetics, and gene expression using Hi-C, promoter Capture Hi-C (PCHi-C), ChIP-seq, and RNA-seq during trans-differentiation of Pre-B cells into macrophages with a β-estradiol inducible C/EBPαER transgene. Within 1h of β-estradiol induction, C/EBPα translocated from the cytoplasm to the nucleus, binding to thousands of promoters and putative regulatory elements, resulting in the downregulation of Pre-B cell-specific genes and induction of macrophage-specific genes. Hi-C results were remarkably consistent throughout trans-differentiation, revealing only a small number of TAD boundary location changes, and A/B compartment switches despite significant changes in the expression of thousands of genes. PCHi-C revealed widespread changes in promoter-anchored loops with decreased interactions in parallel with decreased gene expression, and new and increased promoter-anchored interactions in parallel with increased expression of macrophage-specific genes.
Overall, our data demonstrate that C/EBPα-induced trans-differentiation involves few changes in genome architecture at the level of TADs and A/B compartments, in contrast with widespread reorganization of thousands of promoter-anchored loops in association with changes in gene expression and cell identity.
Sugar is essential for all cellular activities, but at high levels it inhibits growth and development. How plants balance the tradeoffs between the need for sugars and their growth inhibitory effects ...is poorly understood. SHORT-ROOT (SHR) and SCARECROW (SCR) are key regulators of stem cell renewal and radial patterning in the root of Arabidopsis (Arabidopsis thaliana). Recently, we identified direct targets of SHR at the genome scale. Intriguingly, among the top-ranked list, we found a number of genes that are involved in stress responses. By chroma tin immunoprecipitation-polymerase chain reaction (PCR), we showed that SHR and SCR regulate a similar but not identical set of stress response genes. Consistent with this, scr and shr were found to be hypersensitive to abscisic acid (ABA). We further showed that both mutants were hypersensitive to high levels of glucose (Glc) but responded normally to high salinity and osmoticum. The endogenous levels of sucrose, Glc, and fructose were also elevated in shr and scr. Intriguingly, although shr had sugar content and developmental defects similar to those of scr, it was much less sensitive to Glc. Chroma tin immunoprecipitation-PCR and reverse transcription-PCR assays as well as transgenic studies with an ABA-INSENSITIVE2 (ABI4)-ß-glucuronidase reporter construct revealed that in root, SCR, but not SHR, repressed ABI4 and ABI5 directly and specifically in the apical meristem. When combined with abi4, scr became much more tolerant of high Glc. Finally, transgenic plants expressing ABI4 under the control of the SCR promoter manifested a shortroot phenotype. These results together suggest that SCR has a SHR-independent role in mitigating the sugar response and that this role of SCR is important for root growth.
Malignant gliomas are highly lethal cancers dependent on angiogenesis. Critical tumor subpopulations within gliomas share characteristics with neural stem cells. We examined the potential of stem ...cell-like glioma cells (SCLGC) to support tumor angiogenesis. SCLGC isolated from human glioblastoma biopsy specimens and xenografts potently generated tumors when implanted into the brains of immunocompromised mice, whereas non-SCLGC tumor cells isolated from only a few tumors formed secondary tumors when xenotransplanted. Tumors derived from SCLGC were morphologically distinguishable from non-SCLGC tumor populations by widespread tumor angiogenesis, necrosis, and hemorrhage. To determine a potential molecular mechanism for SCLGC in angiogenesis, we measured the expression of a panel of angiogenic factors secreted by SCLGC. In comparison with matched non-SCLGC populations, SCLGC consistently secreted markedly elevated levels of vascular endothelial growth factor (VEGF), which were further induced by hypoxia. In an in vitro model of angiogenesis, SCLGC-conditioned medium significantly increased endothelial cell migration and tube formation compared with non-SCLGC tumor cell-conditioned medium. The proangiogenic effects of glioma SCLGC on endothelial cells were specifically abolished by the anti-VEGF neutralizing antibody bevacizumab, which is in clinical use for cancer therapy. Furthermore, bevacizumab displayed potent antiangiogenic efficacy in vivo and suppressed growth of xenografts derived from SCLGC but limited efficacy against xenografts derived from a matched non-SCLGC population. Together these data indicate that stem cell-like tumor cells can be a crucial source of key angiogenic factors in cancers and that targeting proangiogenic factors from stem cell-like tumor populations may be critical for patient therapy.
Reactive oxygen species （ROS） are harmful to all living organisms and therefore they must be removed to ensure normal growth and development. ROS are also signaling molecules, but so far little is ...known about the mecha- nisms of ROS perception and developmental response in plants. We here report that hydrogen peroxide induces cortex proliferation in the Arabidopsis root and that SPINDLY （SPY）, an O-linked glucosamine acetyltransferase, regulates cortex proliferation by maintaining cellular redox homeostasis. We also found that mutation in the leucine-rich receptor kinase ERECTA and its putative peptide ligand STOMAGEN block the effect of hydrogen peroxide on root cortex proliferation. However, ERECTA and STOMAGEN are expressed in the vascular tissue, whereas extra cortex cells are produced from the endodermis, suggesting the involvement of intercellular signaling~ SPY appears to act downstream of ERECTA, because the spy mutation still caused cortex proliferation in the erecta mutant background. We therefore have not only gained insight into the mechanism by which SPY regulates root development but also uncovered a novel pathway for ROS signal- ing in plants. The importance of redox-mediated cortex proliferation as a protective mechanism against oxidative stress is also discussed.
SHORT-ROOT (SHR) is a key regulator of root growth and development in Arabidopsis (Arabidopsis thaliana). Made in the stele, the SHR protein moves into an adjacent cell layer, where it specifies ...endodermal cell fate; it is also essential for apical meristem maintenance, ground tissue patterning, vascular differentiation, and lateral root formation. Much has been learned about the mechanism by which SHR controls radial patterning, but how it regulates other aspects of root morphogenesis is still unclear. To dissect the SHR developmental pathway, we have determined the genome-wide locations of SHR direct targets using a chroma tin immunoprecipitation followed by microarray analysis method. K-means clustering analysis not only identified additional quiescent center-specific SHR targets but also revealed a direct role for SHR in gene regulation in the pericycle and xylem. Using cell type-specific markers, we showed that in shr, the phloem and the phloem-associated pericycle expanded, whereas the xylem and xylem-associated pericycle diminished. Interestingly, we found that cytokinin level was elevated in shr and that exogenous cytokinin conferred a shr-like vascular patterning phenotype in wild-type root. By chromatin immunoprecipitation-polymerase chain reaction and reverse transcription-polymerase chain reaction assays, we showed that SHR regulates cytokinin homeostasis by directly controlling the transcription of cytokinin oxidase 3, a cytokinin catabolism enzyme preferentially expressed in the stele. Finally, overexpression of a cytokinin oxidase in shr alleviated its vascular patterning defect. On the basis of these results, we suggest that one mechanism by which SHR controls vascular patterning is the regulation of cytokinin homeostasis.
•The dynamic characteristics of the polarization components of the chaotic fiber laser was experimentally studied by permutation entropy, skewness and kurtosis.•The chaotic laser with the higher ...complexity and random characteristics can be obtained by adjusting the polarization.•The spatial resolution for sensing was analyzed by the autocorrelation function.
We experimentally study the complexity of polarization components of chaotic fiber lasers by permutation entropy, skewness and kurtosis. The experimental setup for complexity analysis is composed of the chaotic fiber laser, polarization beam splitter and data-processing systems. The effects of the different polarization states and pump currents on complexity, skewness and kurtosis are experimentally discussed in detail. The result shows chaotic laser with high-complexity can be obtained by analyzing the polarization component of chaotic laser with different polarization. The random characteristics of polarization component of the chaotic fiber laser are analyzed by the autocorrelation function. The spatial resolution is analyzed by combining characteristics of the autocorrelation curve of chaotic fiber laser. The study of the polarization component dynamic characteristics of the chaotic fiber laser is beneficial to obtain chaotic signal with high-complexity and further effectively improve the detection precision of a sensing system based on the chaotic fiber laser.
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