Mandarin (Citrus reticulata) is one of the most important citrus crops worldwide. Its domestication is believed to have occurred in South China, which has been one of the centers of mandarin cultivation for four millennia. We collected natural wild populations of mandarin around the Nanling region and cultivated landraces in the vicinity. We found that the citric acid level was dramatically reduced in cultivated mandarins. To understand genetic basis of mandarin domestication, we de novo assembled a draft genome of wild mandarin and analyzed a set of 104 citrus genomes. We found that the Mangshan mandarin is a primitive type and that two independent domestication events have occurred, resulting in two groups of cultivated mandarins (MD1 and MD2) in the North and South Nanling Mountains, respectively. Two bottlenecks and two expansions of effective population size were identified for the MD1 group of cultivated mandarins. However, in the MD2 group there was a long and continuous decrease in the population size. MD1 and MD2 mandarins showed different patterns of interspecific introgression from cultivated pummelo species. We identified a region of high divergence in an aconitate hydratase (ACO) gene involved in the regulation of citrate content, which was possibly under selection during the domestication of mandarin. This study provides concrete genetic evidence for the geographical origin of extant wild mandarin populations and sheds light on the domestication and evolutionary history of mandarin.

王林发) 186 • Guoping Wang (王国平) 85 • Yanxiang Wang (王雁翔) 85 • Yaqin Wang (王亚琴) 38 • Muhammad Waqas 187 • Tàiyún Wèi (魏太云) 188 • Shaohua Wen (温少华) 85 • Anna E. Whitfield 189 • John V. Williams 190 • Yuri I. Wolf 99 • Jiangxiang Wu (吴建祥) 38 • Lei Xu (徐雷) 138 • Hironobu Yanagisawa (栁澤広 宣) 191 • Caixia Yang (杨彩霞) 69 • Zuokun Yang (杨作坤) 85 • F. Murilo Zerbini 192 • Lifeng Zhai (翟立峰) 193 • Yong-Zhen Zhang (张永振) 220,221 • Song Zhang (张松) 34 • Jinguo Zhang (张靖国) 194 • Zhe Zhang (张哲) 85 • Xueping Zhou (周雪平) 195

Covalent organic frameworks (COFs) have shown extensive applications in energy storage, catalysis, and gas adsorption because of their regular pore structure, flexible topological connectivity, and excellent adjustable functionality. However, their potential applications in colorimetric sensing have not yet been explored. In this study, we synthesized bipyridine-containing covalent organic framework nanosheets (Tp-Bpy NSs) with a regular pore structure and abundant nitrogen-containing functional groups that function as active sites for the in situ generation of AuNPs to form AuNPs@Tp-Bpy. The anchoring of AuNPs onto Tp-Bpy NSs through coordination bonds can significantly enhance the dispersibility, stability, and catalytic activity of the AuNPs. We find that the synergistic effect of increased mimetic activity of gold amalgam and the higher access probability of Hg 2+ provided by Tp-Bpy nanosheets makes the AuNPs@Tp-Bpy nanocomposite exhibit a high performance for the detection of Hg 2+ with an ultralow detection limit of 0.33 nM. This sensing platform has been successfully used for the sensitive and stable detection of Hg 2+ in various environmental samples. The present study extends the application of COFs and opens a new frontier for the design of novel nanocomposites for a variety of potential applications.

The model of the molecular weight distribution (MWD) of polypropylene produced in a loop reactor is established. The simulated MWD data of the polymers produced in steady-state polymerizations agree with the actual data collected from certain plant. The simulated weight-average molecular weight data also agree with the plant data in start-up processes. Furthermore, the model can be used to simulate the influence of the operation parameters on the MWD of the polymers produced in the steady-state polymerizations as well as the dynamic polymerizations. The simulated results of the steady state polymerizations show the MWD width of polypropylene decreases with the increase of both the propylene flow and the hydrogen flow, but increases with the increase of the catalyst flow. We also find the weight fraction of the polymers with short chains increases with the increase of both the propylene flow and the hydrogen flow, meanwhile, a small shift of the MWD curve to long chains can also be found as the catalyst flow increases. In the dynamic polymerizations, simulations indicate the MWD width and the weight fraction of the polymers with long chains all decrease in both of the start-up process and the end-up process of the polymerizations

This study reports a novel and convenient bimodal method for label-free and signal-off detection of arsenate in environmental samples. Cobalt oxyhydroxide (CoOOH) nanoflakes with facile preparation and intrinsic peroxidase-like activity as nanozyme can efficiently catalyze the conversion of chromogenic substrate such as 2,2′-azinobis­(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with the presence of H2O2 into green-colored oxidation products. CoOOH nanoflakes can specifically bind with arsenate via electrostatic attraction and As–O bond interaction, which gives rise to inhibition of the peroxidase-like activity of CoOOH. Thus, through arsenate specific inhibition of CoOOH nanozyme toward ABTS catalysis, a simple colorimetric method was developed for arsenate detection with a detection limit of 3.72 ppb. Based on the system of CoOOH nanozyme and ABTS substrate, this colorimetric method can be converted into an electrochemical sensor for arsenate assay by the utilization of CoOOH nanoflake-modified electrode. The electrochemical measurement can be realized by chronoamperometry, which showed more sensitive and a lower limit of detection as low as 56.1 ppt. The applicability of this bimodal method was demonstrated by measuring arsenate and total arsenic in different real samples such as natural waters and soil extracted solutions, and the results are of satisfactory accuracy as confirmed by inductively coupled plasma mass spectrometry analysis. The bimodal strategy offers obvious advantages including a label-free step, convenient operation, on-site assay, low cost, and high sensitivity, which is promising for reliable detection of arsenate and total arsenic in environmental samples.