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Polycomb group (PcG) proteins maintain cell identity by repressing gene expression during development. Surprisingly, emerging studies have recently reported that a number of PcG proteins directly activate gene expression during cell fate determination process. However, the mechanisms by which they direct gene activation in pluripotency remain poorly understood. Here, we show that Phc1, a subunit of canonical polycomb repressive complex 1 (cPRC1), can exert its function in pluripotency maintenance via a PRC1-independent activation of Nanog. Ablation of Phc1 reduces the expression of Nanog and overexpression of Nanog partially rescues impaired pluripotency caused by Phc1 depletion. We find that Phc1 interacts with Nanog and activates Nanog transcription by stabilizing the genome-wide chromatin interactions of the Nanog locus. This adds to the already known canonical function of PRC1 in pluripotency maintenance via a PRC1-dependent repression of differentiation genes. Overall, our study reveals a function of Phc1 to activate Nanog transcription through regulating chromatin architecture and proposes a paradigm for PcG proteins to maintain pluripotency. Phc1 is a subunit of the polycomb repressive complex 1 (PRC1), which represses gene expression during development. Here the authors show that Phc1 acts independently from PRC1 to activate Nanog transcription by stabilizing genome-wide chromatin interactions of the Nanog locus, and in turn stabilize pluripotency. [ABSTRACT FROM AUTHOR]

A proteomic analysis combining photosynthesis-related key enzymes measurement and mRNA level analysis was used to investigate the variations of proteins involved in the photosynthetic apparatus in flag leaves of high-yield rice LYPJ during senescence under field conditions. The stability of chlorophyll-protein complexes of thylakoid membranes was measured by BN-PAGE system. Our findings revealed that the LHCII complexes were more stable than FF-ATPase and Cy b /f complexes. Thylakoid membranes proteins during the senescence stage were separated by two-dimensional gel electrophoresis. We identified 13 photosynthesis-related proteins (a fivefold or greater variation), including electron transport, Calvin-Benson cycle and chloroplast protease during senescence of flag leaves. Moreover, our data showed that Ca-ATPase was more stable during senescence of flag leaves in rice, compared to Mg-ATPase. In enzymes activities analyses, it was observed that a little increment of C4 photosynthetic enzymes activities at the beginning of flag leaves senescence might compensate, to some degree, for the larger reductions in Rubisco activity, confirmed by quantitative RT-PCR analysis. [ABSTRACT FROM AUTHOR]

The current study compares responses to open field and shade enclosure condition (plastic shading nets were used to imitate a natural shading rate) to test the possible benefit of shading in terms of physiological and growth characteristics in Ginkgo biloba L. during the reproductive stage in summer. Compared with the net shade treated plants (NS-plants), the open-field plants (O-plants) contained lower chlorophyll (Chl) a + b content and Chl a/b ratio, and exhibited a decreased ratio of Chl/Car. Results showed that the chlorophyll fluorescence characteristics including maximum PSII photochemical efficiency ( F /F), potential electron transport per excited leaf cross-section (ET/CS), potential electron transport per PSII reaction center (ET/RC), dissipation per excited leaf cross-section (DI/CS), dissipation per PSII reaction center (DI/RC), and overall performance index of PSII photochemistry on absorbtion basis (PI) were altered by the net shade treatment. It was observed that the grana were illegible and difficult to distinguish by transmission electron microscopy, especially, in the cells of O-plants in which phenols were observed in the vacuole. The phenomenon of photoinhibition induced by excessive irradiance was confirmed by the abnormally high levels of the reactive oxygen species. Moreover, antioxidant enzymes activities were induced by high irradiance in the ginkgo leaves. In addition, significant differences were observed in the fresh weight and dry weight of leaves and seeds. Comparison of the variation of underlying physiological and biochemical mechanisms suggested that there was a better efficiency of ginkgo plants under artificial net shade conditions. Therefore, ginkgo plant would be best grown at 30-35 % of natural irradiance in summer months to be more profitably harvested and then meet the increasing demand of leaves and seeds. [ABSTRACT FROM AUTHOR]