Mechanism of primary Si and Fe-segregation for a hypereutectic 90 wt.%Si-Ti alloy melt in directional solidification via electromagnetism

The electromagnetic directional solidification(DS)phase separation experiments of high silicon 90 wt.%Si–Ti alloy were performed under various pulling-down speeds.The results showed that Si enriched layer,Si+TiSi_(2)-rich layer and Si–Ti–Fe alloy layer appeared successively in axial direction of ingot after electromagnetic DS of 90 wt.%Si–Ti alloy melt at different pulling-down speeds.Separation of primary Si and segregation mechanism of metal impurities(Fe)during the electromagnetic DS process were controlled by pulling-down speed of ingot and electromagnetic stirring.When pulling-down speed was 5μm/s,minimum thickness of the Si enriched layer was 29.4 mm,and the highest content of primary Si in this layer was 92.46 wt.%;meanwhile,the highest removal rate of Fe as metal impurity was 92.90%.The type of inclusions in the Si enriched layer is determined by Fe content of segregated Si enriched layer.When the pulling-down speed was 5μm/s,the inclusions in the Si enriched layer were TiSi_(2).Finally,when the pulling-down speed reached greater than 5μm/s,the inclusions in the Si enriched layer evolved into TiSi_(2)+τ_(5).

Dynamic and Coordinated Expression Changes of Rice Small RNAs in Response to Xanthomonas oryzae pv.oryzae

Endogenous small RNAs are newly identified players in plant immune responses, yet their roles in rice （Oryza sativa） responding to pathogens are still less understood, especially for pathogens that can cause severe yield losses. We examined the small RNA expression profiles of rice leaves at 2, 6, 12, and 24 hours post infection ofXanthomonas oryzae pv. oryzae （Xoo） virulent strain PXO99, the causal agent of rice bacterial blight disease. Dynamic expression changes of some miRNAs and trans-acting siRNAs were identified, together with a few novel miRNA targets, including an RLK gene targeted by osa-miR159a. 1. Coordinated expression changes were observed among some small RNAs in response to Xoo infection, with small RNAs exhibiting the same expression pattern tended to regulate genes in the same or related signaling pathways, including auxin and GA signaling pathways, nutrition and defense-related pathways. These findings reveal the dynamic and complex roles of small RNAs in rice-Xoo interactions, and identify new targets for regulating plant responses to Xoo.

Locus- and cell type-specific epigenetic switching during cellular differentiation in mammals

BACKGROUND： Epigenomic reconfiguration, including changes in DNA methylation and histone modifications, is crucial for the differentiation of embryonic stem cells （ESCs） into somatic cells. However, the extent to which the epigenome is reconfigured and the interplay between components of the epigenome during cellular differentiation remain poorly defined. METHODS： We systematically analyzed and compared DNA methylation, various histone modification, and transcriptome profiles in ESCs with those of two distinct types of somatic cells from human and mouse. RESULTS： We found that global DNA methylation levels are lower in somatic cells compared to ESCs in both species. We also found that 80% of regions with histone modification occupancy differ between human ESCs and the two human somatic cell types. Approximately 70% of the reconfigurations in DNA methylation and histone modifications are locus- and cell type- specific. Intriguingly, the loss ofDNA methylation is accompanied by the gain of different histone modifications in a locus- and cell type-specific manner. Further examination of transcriptional changes associated with epigenetic reconfiguration at promoter regions revealed an epigenetic switching for gene regulation--a transition from stable gene silencing mediated by DNA methylation in ESCs to flexible gene repression facilitated by repressive histone modifications in somatic cells. CONCLUSIONS： Our findings demonstrate that the epigenome is reconfigured in a locus- and cell type-specific manner and epigenetic switching is common during cellular differentiation in both human and mouse.