The emergence of apomixis-the transition from sexual to asexual reproduction-is a prominent feature of modern citrus. Here we de novo sequenced and comprehensively studied the genomes of four representative citrus species. Additionally, we sequenced 100 accessions of primitive, wild and cultivated citrus. Comparative population analysis suggested that genomic regions harboring energy- and reproduction-associated genes are probably under selection in cultivated citrus. We also narrowed the genetic locus responsible for citrus polyembryony, a form of apomixis, to an 80-kb region containing 11 candidate genes. One of these, CitRWP, is expressed at higher levels in ovules of polyembryonic cultivars. We found a miniature inverted-repeat transposable element insertion in the promoter region of CitRWP that cosegregated with polyembryony. This study provides new insights into citrus apomixis and constitutes a promising resource for the mining of agriculturally important genes.

Carotenoids and apocarotenoids act as phytohormones and volatile precursors that influence plant development and confer aesthetic and nutritional value critical to consumer preference. Citrus fruits display considerable natural variation in carotenoid and apocarotenoid pigments. In this study, using an integrated genetic approach we revealed that a 5 0 cis-regulatory change at CCD4b encoding CAROTENOID CLEAVAGE DIOXYGENASE 4b is a major genetic determinant of natural variation in C 30 apocarotenoids responsible for red coloration of citrus peel. Functional analyses demonstrated that in addition the known role in synthesizing b-citraurin, CCD4b is also responsible for the production of another important C 30 apocarotenoid pigment, b-citraurinene. Furthermore, analyses of the CCD4b promoter and transcripts from various citrus germplasm accessions established a tight correlation between the presence of a putative 5 0 cis-regulatory enhancer within an MITE transposon and the enhanced allelic expression of CCD4b in C 30 apocarotenoid-rich red-peeled accessions. Phylogenetic analysis provided further evidence that functional diversification of CCD4b and naturally occurring variation of the CCD4b promoter resulted in the stepwise evolution of red peels in mandarins and their hybrids. Taken together, our findings provide new insights into the genetic and evolutionary basis of apocarotenoid diversity in plants, and would facilitate breeding efforts that aim to improve the nutritional and aesthetic value of citrus and perhaps other fruit crops.

Novel fluorescent europium(III) chelate-doped silica nanoparticles were prepared and characterized as a new type of fluorescence probe for quantitative bioassay. The preparation was carried out in a water-in-oil (w/o) microemulsion consisting of a strongly fluorescent Eu 31 chelate, 4,4'-bis(1@,1@,1@,2@,2@,3@,3@-heptafluoro-4@,6@-hexanedion-6@-yl)-o-terphenyl-Eu 31 (BHHT-Eu 31 ), surfactant (Triton X-100), co-surfactant (n-hexanol, n-heptanol or n-octanol), aqueous phase (H 2 O or D 2 O) and oil phase (cyclohexane) by controlling the hydrolysis of tetraethylorthosilicate (TEOS). The effects of different co-surfactants and aqueous phases on the size and fluorescence lifetime of the nanoparticles were investigated. The results reveal that the size of the nanoparticles is decreased with a change of co-surfactants from n-hexanol to n-octanol, and the fluorescence lifetime of the nanoparticles is increased with a change of aqueous phase from H 2 O to D 2 O. A new method was established for the surface modification and bioconjugation of the nanoparticles. Nanoparticle-labeled streptavidin (SA) was used for the time-resolved fluoroimmunoassay of human hepatitis B surface antigen (HBsAg). The result shows that the new fluorescent europium(III) chelate-doped silica nanoparticles are suitable to be used as a fluorescence probe for highly sensitive bioassays.

No abstract

Oil produced by castor ( Ricinus communis ) has broad industrial applications. However, knowledge on the genetic diversity, especially genetic alterations that occurred during domestication and subsequent traits selection, of this oil crop is limited. Here, our population genomics analyses show that the Chinese castors have developed a geographic pattern, classified into the southern-, the middle-, and the northern-China groups. We detect a number of candidate genomic loci that are associated with the selection signals during the geographical differentiation and domestication. Using genome-wide association analysis, we identify candidate genes associated with nine agronomically important traits. One of the candidate genes encoding a glycosyltransferase related to cellulose and lignin biosynthesis is associated with both capsule dehiscence and endocarp thickness. We hypothesize that the abundance of cellulose or lignin in endocarp is an important factor for capsule dehiscence. Our results provide foundation for castor breeding and genetic study.

Magnetic resonance imaging (MRI) is a powerful medical diagnostic imaging modality for integrin targeted imaging, which uses the magnetic resonance of tissue water protons to display tissue anatomic structures with high spatial resolution. Contrast agents are often used in MRI to highlight specific regions of the body and make them easier to visualize. There are four main classes of MRI contrast agents based on their different contrast mechanisms, including T1, T2, chemical exchange saturation transfer (CEST) agents, and heteronuclear contrast agents. Integrins are an important family of heterodimeric transmembrane glycoproteins that function as mediators of cell-cell and cell-extracellular matrix interactions. The overexpressed integrins can be used as the molecular targets for designing suitable integrin targeted contrast agents for MR molecular imaging. Integrin targeted contrast agent includes a targeting agent specific to a target integrin, a paramagnetic agent and a linker connecting the targeting agent with the paramagnetic agent. Proper selection of targeting agents is critical for targeted MRI contrast agents to effectively bind to integrins for in vivo imaging. An ideal integrin targeted MR contrast agent should be non-toxic, provide strong contrast enhancement at the target sites and can be completely excreted from the body after MR imaging. An overview of integrin targeted MR contrast agents based on small molecular and macromolecular Gd(III) complexes, lipid nanoparticles and superparamagnetic nanoparticles is provided for MR molecular imaging. By using proper delivery systems for loading sufficient Gd(III) chelates or superparamagnetic nanoparticles, effective molecular imaging of integrins with MRI has been demonstrated in animal models.

No abstract

Recently, several kinds of nanometer-sized luminescent materials, such as semiconductor nanocrystals (quantum dots), plasmon-resonant nanoparticles, and luminophore-doped silica nanoparticles, have been developed and used as luminescence probes for biological detections and biotechnologies.