Newly Developed Genomic SSRs Reveal Genetic Diversity in Wild and Cultivated Amorphophallus albus Germplasms

Plant Molecular Biology Reporter - Amorphophallus albus is a crop plant of great economic value in glucomannan production. However, the cultivation industry surrounding this plant is so new that no...     

Linkage Mapping Identifies the Sex Determining Region as a Single Locus in the Pennate Diatom Seminavis robusta

The pennate diatom Seminavis robusta, characterized by an archetypical diatom life cycle including a heterothallic mating system, is emerging as a model system for studying the molecular regulation of the diatom cell and life cycle. One of its main advantages compared with other diatom model systems is that sexual crosses can be made routinely, offering unprecedented possibilities for forward genetics. To date, nothing is known about the genetic basis of sex determination in diatoms. Here, we report on the construction of mating type-specific linkage maps for S. robusta, and use them to identify a single locus sex determination system in this diatom. We identified 13 mating type plus and 15 mating type minus linkage groups obtained from the analysis of 463 AFLP markers segregating in a full-sib family, covering 963.7 and 972.2 cM, respectively. Five linkage group pairs could be identified as putative homologues. The mating type phenotype mapped as a monogenic trait, disclosing the mating type plus as the heterogametic sex. This study provides the first evidence for a genetic sex determining mechanism in a diatom.     

Haplotype Frequency Distribution and Linkage Disequilibrium Analysis of Single Nucleotide Polymorphisms at the Human FMO3 Gene Locus

We analyzed flavin-containing monooxygenase 3 (FMO3) polymorphisms, haplotype structure, and linkage disequilibrium (LD) in 256 Han Chinese and 50 African-American individuals to compare their haplotype frequencies and LD with other world populations. For the Han Chinese, genotyping of three haplotype tag single nucleotide polymorphisms (E158K, V257M, and E308G) was performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism. For the African-Americans, genotyping of all coding exons was performed by modified PCR-single strand conformational polymorphism. Haplotype frequencies, LD, and evolutionary rates were inferred and estimated computationally. There were significant differences in haplotype frequency distribution and LD pattern among Han Chinese, African-Americans, and other world populations. Four major haplotypes of Han Chinese were EVE, KVE, EME, and EVG. Two major haplotypes of African-Americans were EVE and KVE. We found that sites 158 and 257 are in significant LD in both populations. This is the first report comparing FMO haplotypes and LD of Han Chinese with African-Americans. The data presented here justify further pharmacogenetic studies for potentially optimizing recommended drug dosages and evaluating relationships with disease processes.     

A first AFLP-Based Genetic Linkage Map for Brine Shrimp Artemia franciscana and Its Application in Mapping the Sex Locus

We report on the construction of sex-specific linkage maps, the identification of sex-linked markers and the genome size estimation for the brine shrimp Artemia franciscana. Overall, from the analysis of 433 AFLP markers segregating in a 112 full-sib family we identified 21 male and 22 female linkage groups (2n = 42), covering 1,041 and 1,313 cM respectively. Fifteen putatively homologous linkage groups, including the sex linkage groups, were identified between the female and male linkage map. Eight sex-linked AFLP marker alleles were inherited from the female parent, supporting the hypothesis of a WZ–ZZ sex-determining system. The haploid Artemia genome size was estimated to 0.93 Gb by flow cytometry. The produced Artemia linkage maps provide the basis for further fine mapping and exploring of the sex-determining region and are a possible marker resource for mapping genomic loci underlying phenotypic differences among Artemia species.     

厚朴野生种与栽培种花不同部位香气成分分析

以厚朴野生种和栽培种苞片刚裂开的花苞为试材,采用固相微萃取和气相色谱—质谱(GC/MS)分析技术对其进行香气成分和相对含量的测定,比较分析了花朵不同部位香气成分的差异。结果表明：厚朴野生种共有39种香气成分,雌雄蕊中26种,花瓣中22种,栽培种中75种香气成分,雌雄蕊中49种,花瓣中54种。萜烯类是两种厚朴花苞中最重要的香气化合物,莰烯、罗勒烯异构体混合物、石竹烯、芳樟醇是野生种和栽培种中共有的相对含量较高的香气成分。厚朴野生种和栽培种间以及同种厚朴雌雄蕊与花瓣之间的香气成分的种类和相对含量差异显著。     

Contrasting Mode of Evolution at a Coat Color Locus in Wild and Domestic Pigs

Despite having only begun ~10,000 years ago, the process of domestication has resulted in a degree of phenotypic variation within individual species normally associated with much deeper evolutionary time scales. Though many variable traits found in domestic animals are the result of relatively recent human-mediated selection, uncertainty remains as to whether the modern ubiquity of long-standing variable traits such as coat color results from selection or drift, and whether the underlying alleles were present in the wild ancestor or appeared after domestication began. Here, through an investigation of sequence diversity at the porcine melanocortin receptor 1 (MC1R) locus, we provide evidence that wild and domestic pig (Sus scrofa) haplotypes from China and Europe are the result of strikingly different selection pressures, and that coat color variation is the result of intentional selection for alleles that appeared after the advent of domestication. Asian and European wild boar (evolutionarily distinct subspecies) differed only by synonymous substitutions, demonstrating that camouflage coat color is maintained by purifying selection. In domestic pigs, however, each of nine unique mutations altered the amino acid sequence thus generating coat color diversity. Most domestic MC1R alleles differed by more than one mutation from the wild-type, implying a long history of strong positive selection for coat color variants, during which time humans have cherry-picked rare mutations that would be quickly eliminated in wild contexts. This pattern demonstrates that coat color phenotypes result from direct human selection and not via a simple relaxation of natural selective pressures.     

Striking Natural Diversity in Glandular Trichome Acylsugar Composition Is Shaped by Variation at the Acyltransferase2 Locus in the Wild Tomato Solanum habrochaites

Acylsugars are polyesters of short- to medium-length acyl chains on sucrose or glucose backbones that are produced in secretory glandular trichomes of many solanaceous plants, including cultivated tomato (Solanum lycopersicum). Despite their roles in biotic stress adaptation and their wide taxonomic distribution, there is relatively little information about the diversity of these compounds and the genes responsible for their biosynthesis. In this study, acylsugar diversity was assessed for 80 accessions of the wild tomato species Solanum habrochaites from throughout the Andes Mountains. Trichome metabolites were analyzed by liquid chromatography-time of flight-mass spectrometry, revealing the presence of at least 34 structurally diverse acylsucroses and two acylglucoses. Distinct phenotypic classes were discovered that varied based on the presence of glucose or sucrose, the numbers and lengths of acyl chains, and the relative total amounts of acylsugars. The presence or absence of an acetyl chain on the acylsucrose hexose ring caused clustering of the accessions into two main groups. Analysis of the Acyltransferase2 gene (the apparent ortholog of Solyc01g105580) revealed differences in enzyme activity and gene expression correlated with polymorphism in S. habrochaites accessions that varied in acylsucrose acetylation. These results are consistent with the hypothesis that glandular trichome acylsugar acetylation is under selective pressure in some populations of S. habrochaites and that the gene mutates to inactivity in the absence of selection.Trichomes are specialized epidermal cells that protrude from the surface of a variety of plant tissues. They are thought to protect against environmental stresses such as herbivory (Kang et al., 2010a; Weinhold and Baldwin, 2011), loss of water through transpiration, and UV irradiation (Zhou et al., 2007). In particular, secreting glandular trichomes (SGTs) serve as “chemical factories” where specialized metabolites are produced, stored, or volatized (Wagner, 1991; Schilmiller et al., 2008, 2010a). In addition, SGTs produce and secrete proteins on the plant surface for insect protection (Yu et al., 1992; Thipyapong et al., 1997) and pathogen defense (Shepherd et al., 2005). SGTs also contribute to the taste and smell of plants by releasing volatile metabolites. For example, the distinctive aromas of many Mediterranean herbs of the Lamiaceae (mint family) derive from SGTs (Schilmiller et al., 2008), and compounds from the glands of hops (Humulus lupulus in the Cannabaceae) contribute to beer flavor and aroma (Wang et al., 2008). Furthermore, a number of SGT-borne metabolites are commercially valuable, especially for pharmaceutical purposes. For example, artemisinin, a widely used antimalarial, is a sesquiterpene lactone from the trichomes of Artemisia annua (Liu et al., 2011). In addition to their value in foods and medicines, trichomes provide excellent models for analyzing biosynthetic enzymes and pathways (Schilmiller et al., 2008, 2009, 2012b; Bohlmann and Gershenzon, 2009; Sallaud et al., 2009).Plants in the genus Solanum include important crop species such as potato (Solanum tuberosum), eggplant (Solanum melongena), and tomato (Solanum lycopersicum). Previous studies reported that SGTs of cultivated tomato and its wild relatives accumulate high levels of exudates containing a variety of specialized metabolites, for example flavonoids, alkaloids, and terpenoids (Wagner, 1991; Schilmiller et al., 2008, 2010a; McDowell et al., 2011). Cultivated tomato and its wild relatives have morphologically and chemically diverse trichomes. For example, Luckwill (1943) defined seven morphologically distinguishable types of trichomes in plants of this genus, including four glandular types (types 1, 4, 6, and 7; Supplemental Fig. S1; for more Solanum spp. trichome images, see Kang et al., 2010a, 2010b). The presence of specific types of trichomes and their densities vary across species and even within a single plant according to tissue types, developmental stages, and environmental conditions (Werker, 2000; Li et al., 2004). These morphologically distinct SGTs vary in the amounts and types of metabolites that they produce, accumulate, and/or secrete (Werker, 2000). For example, S. lycopersicum M82 leaf type 6 SGTs accumulate the sesquiterpenes β-caryophyllene and α-humulene, while the glands on the stem lack these metabolites (Schilmiller et al., 2010b). There are also species- and accession-specific differences in SGT metabolite profiles. For instance, methylketones accumulate in type 6 glands of a subset of Solanum habrochaites accessions (Fridman et al., 2005; Yu et al., 2010). Similarly, acylglucoses are highly abundant in type 4 glands of Solanum pennellii LA0716, while acylsucroses predominate in S. lycopersicum and S. habrochaites (Shapiro et al., 1994; McDowell et al., 2011). The chemical and morphological diversity of trichomes in different Solanum species and accessions makes the genus an attractive target for the identification of diverse trichome-borne metabolites and the major biosynthetic pathways responsible for their synthesis operating in each trichome type.The value of the comparative metabolomics approach in trichomes was recently demonstrated in studies of Solanum spp. trichome monoterpene and sesquiterpene biosynthesis (Bohlmann and Gershenzon, 2009; Sallaud et al., 2009; Schilmiller et al., 2009). It was discovered that S. lycopersicum SGTs synthesize monoterpenes from the cis-prenyldiphosphate intermediate neryldiphosphate (Sallaud et al., 2009; Schilmiller et al., 2009). This is contrary to the previous paradigm, where the trans-prenyldiphosphate geranyldiphosphate was considered the universal intermediate for monoterpene biosynthesis. An analogous example of biosynthetic innovation was reported for SGTs of S. habrochaites LA1777 (Sallaud et al., 2009), shown to produce sesquiterpenes in the plastid using the all-cis-prenyldiphosphate substrate Z,Z-farnesyldiphosphate. This is counter to the commonly described cytosolic sesquiterpene pathway, which uses the all-trans-sesquiterpene synthase substrate E,E-farnesyldiphosphate. Furthermore, a recent study demonstrated chemical diversity of trichome terpenes in geographically distinct S. habrochaites accessions associated with the evolution of terpene synthases, revealing how the plasticity of biosynthetic enzymes contributes to chemical complexity and diversity (Gonzales-Vigil et al., 2012). These observations suggest that trichome specialized metabolism is evolutionarily plastic, perhaps due to selective pressure from insects or other environmental stress agents.Acylsugars are sticky exudates made in SGTs that are thought to physically or chemically improve plant defense (Mirnezhad et al., 2010; Weinhold and Baldwin, 2011). Results from the literature indicate strong acylsugar diversity in various Solanum spp. trichomes (Schilmiller et al., 2010a, 2010b; McDowell et al., 2011). Acylsugars are categorized as either Suc or Glc esters based on the type of sugar core (Fig. 1), and they also have varying numbers and lengths of acyl chains decorating the sugar moiety. In particular, S. pennellii accumulates enormous amounts of acylsugars, up to 20% of leaf dry weight (Fobes et al., 1985). In addition, previously published data showed that total acylsugars in geographically distinct S. pennellii accessions vary in quantity, the proportion of Suc or Glc backbones, and the overall types of fatty acid esters (FAs) on the sugars (Shapiro et al., 1994). However, this study did not identify specific acylsugar types.Open in a separate windowFigure 1.Structural classes of acylsugars in Solanum species. A, Schematic structure of an acylglucose. The structure shown depicts a Glc triester composed of Glc and three acyl chains with various numbers of carbons represented as R. B, Schematic structure of an acylsucrose. The proposed structure shows a Suc tetraester with three acyl chains on the Glc ring and one on the Fru ring. If the sugar moiety is decorated with three, four, or five acyl chains, it is referred to as a Suc triester, tetraester, or pentaester, respectively. The positions of the acyl chains are currently unknown, with the exception of the most abundant acylsugar in cultivated tomato (M82) that was structurally characterized by NMR (Schilmiller et al., 2010a). In addition, a few acylsugars were isolated and reported from S. habrochaites and other species by King et al. (1990, 1993). Note the changes in nomenclature since these papers were published: Lycopersicum typicum LA1777 is now called S. habrochaites LA1777, and Lycopersicum hirsutum has been changed to S. habrochaites.To explore the detailed acylsugar chemotypes within accessions of one species, we focused on 80 accessions collected throughout the geographical range of S. habrochaites in Peru and Ecuador (Supplemental Table S1). We describe differences in sugar backbone as well as numbers and lengths of acyl chains, including the presence or absence of an acetyl group, which we found to be a major difference in accessions from the southern and northern Andes Mountains. The recent identification of the acyltransferase2 enzyme (SlAT2; encoded by Solyc01g105580), involved in acylsucrose biosynthesis in S. lycopersicum (Schilmiller et al., 2012a), permitted a test of the hypothesis that differences in expression or activity of this enzyme play an important role in the chemical diversity observed. The results extend previous evidence that Solanum spp. SGT chemistry is highly dynamic (Gonzales-Vigil et al., 2012) and show that the AT2 gene is surprisingly diverse across populations of S. habrochaites.     

Genetic Structure and Diversity in Wild and Cultivated Populations of the Mangrove Oyster Crassostrea gasar from Southern Brazil

Marine Biotechnology - The mangrove oyster (Crassostrea gasar) is Brazil’s second most cultured species and presents a high potential for aquaculture. However, artificial selection in a...     

Microscopic and Molecular Studies of the Diversity of Free-Living Protozoa in Meat-Cutting Plants

The diversity of free-living protozoa in five meat-cutting plants was determined. Light microscopy after enrichment culturing was combined with sequencing of PCR-amplified, denaturing gradient gel electrophoresis (DGGE)-separated 18S rRNA gene fragments, which was used as a fast screening method. The general results of the survey showed that a protozoan community of amoebae, ciliates, and flagellates was present in all of the plants. Protozoa were detected mainly in floor drains, in standing water on the floor, on soiled bars of cutting tables, on plastic pallets, and in out-of-use hot water knife sanitizers, but they were also detected on surfaces which come into direct contact with meat, such as conveyer belts, working surfaces of cutting tables, and needles of a meat tenderizer. After 7 days of incubation at refrigerator temperature, protozoa were detected in about one-half of the enrichment cultures. Based on microscopic observations, 61 morphospecies were found, and Bodo saltans, Bodo spp., Epistylis spp., Glaucoma scintillans, Petalomonas spp., Prodiscophrya collini, and Vannella sp. were the most frequently encountered identified organisms. Sequencing of DGGE bands resulted in identification of a total of 49 phylotypes, including representatives of the Amoebozoa, Chromalveolata, Excavata, Opisthokonta, and Rhizaria. Sequences of small heterotrophic flagellates were affiliated mainly with the Alveolata (Apicomplexa), Stramenopiles (Chrysophyceae), and Rhizaria (Cercozoa). This survey showed that there is high protozoan species richness in meat-cutting plants and that the species included species related to known hosts of food-borne pathogens.     

Ascertainment Bias and the Pattern of Nucleotide Diversity at the Human ALDH2 Locus in a Japanese Population

Many East Asian human populations harbor a high-frequency deficiency allele for the aldehyde dehydrogenase 2 (ALDH2) enzyme, a critical protein involved in the metabolism of ethanol. Here we use resequencing and long-range SNP haplotype data from a Japanese sample to test whether patterns of nucleotide diversity and linkage disequilibrium at this locus are compatible with a standard neutral model of evolution. Examination of the pattern of polymorphism at a locus such as this, where the frequency of a common allele is known a priori, introduces an ascertainment bias that must be corrected for in analyses of the frequency spectrum of polymorphisms. We apply a flexible and generally applicable simulation approach to correct for this bias in our ALDH2 data and, also, to explore the effect of bias on the commonly used summary statistics Tajima’s D, Fu and Li’s D, and Fay and Wu’s H. Our study finds no evidence that the pattern of genetic variation at ALDH2 differs from that expected under a standard neutral model. However, our general examination of ascertainment bias indicates that a priori knowledge of segregating alleles greatly affects the expected distributions of summary statistics. Under many parameter combinations we find that ascertainment bias introduces an elevated rate of false positives when summary statistics are used to test for deviations from a standard neutral model. However, we also show that over a wide range of conditions the power of all summary statistics can be greatly increased by incorporating prior knowledge of segregating alleles. [Reviewing Editor: Dr. Martin Kreitman]     

Elucidation of Molecular Identity of the W3 Locus and Its Implication in Determination of Flower Colors in Soybean

The wide range of flower colors in soybean is controlled by six independent loci (W1, W2, W3, W4, Wm, and Wp). Among these loci, mutations in the W3 locus under the w4 allelic background (i.e., w3w4) produce near-white flowers, while the W3w4 genotype produces purple throat flowers. Although a gene encoding dihydroflavonol 4-reductase, DFR1, has been known to be closely associated with the W3 locus, its molecular identity has not yet been characterized. In the present study, we aimed to determine whether DFR1 is responsible for allelic variations in the W3 locus. On the basis of the sequence of a DFR probe, Glyma.14G072700 was identified as a candidate gene for DFR1, and nucleotide sequences of Glyma.14G072700 from cultivars with previously validated genotypes for the W3 locus were determined. As a result, a number of nucleotide polymorphisms, mainly single-base substitutions, between both coding and 5′-upstream region sequences of the W3 and w3 alleles were identified. Among them, an indel of 311-bp in the 5′-upstream region was noteworthy, since the Glyma.14G072700 in all the w3 alleles examined contained the indel, whereas that in all the W3 alleles did not; the former was barely expressed, but the latter was well expressed. These results suggest that Glyma.14G072700 is likely to correspond to DFR1 for the W3 locus and that its expression patterns may lead to allelic color phenotypes of W3 and w3 alleles under the w4 allelic background.     

Multilocus Patterns of Nucleotide Diversity, Population Structure and Linkage Disequilibrium in Boechera stricta, a Wild Relative of Arabidopsis

Information about polymorphism, population structure, and linkage disequilibrium (LD) is crucial for association studies of complex trait variation. However, most genomewide studies have focused on model systems, with very few analyses of undisturbed natural populations. Here, we sequenced 86 mapped nuclear loci for a sample of 46 genotypes of Boechera stricta and two individuals of B. holboellii, both wild relatives of Arabidopsis. Isolation by distance was significant across the species range of B. stricta, and three geographic groups were identified by structure analysis, principal coordinates analysis, and distance-based phylogeny analyses. The allele frequency spectrum indicated a genomewide deviation from an equilibrium neutral model, with silent nucleotide diversity averaging 0.004. LD decayed rapidly, declining to background levels in ~10 kb or less. For tightly linked SNPs separated by <1 kb, LD was dependent on the reference population. LD was lower in the specieswide sample than within populations, suggesting that low levels of LD found in inbreeding species such as B. stricta, Arabidopsis thaliana, and barley may result from broad geographic sampling that spans heterogeneous genetic groups. Finally, analyses also showed that inbreeding B. stricta and A. thaliana have ~45% higher recombination per kilobase than outcrossing A. lyrata.     

珍稀药用植物红根草野生及离体快繁群体的遗传多样性

红根草是一个有重要药用价值的珍稀濒危药材植物。为了更好地了解红根草野生和组培快繁种质的遗传多样性信息,本文用RAPD和ISSR分子标记技术,对红根草4个野生种群及一个离体快繁群体进行遗传多样性分析,为物种保护和繁育提供理论依据。结果显示,在物种水平上,该物种的遗传多样性水平中等,Nei基因多样性指数（H）、Shannon信息多样性指数（I）和多态性位点百分率（PPL）分别为0.237/0.248（RAPD/ISSR,下同）、0.365/0.380和78.4%/81.1%;遗传变异大多数（70.5%/81.5%）发生在种群内、少部分（29.5%/18.5%）发生在种群间;野生种群的基因流为1.21/2.20,但UPGMA聚类分析结果表明,距离35km以上的种群遗传分化明显,因此推测基因流动主要存在于种群内,地理距离是种群分化的主要原因。在居群水平上,H、I和PPL三项遗传多样性参数分别为0.167/0.202、0.253/0.303和51.7%/58.0%;离体快繁群体的RAPD分析结果显示,其遗传多样性高于其原野生种群,这一结果暗示,离体快繁过程中可能发生了体细胞变异,这些变异与RAPD-PCR区域有关。     

Nucleotide Diversity and Molecular Evolution of the <Emphasis Type="Italic">ALK</Emphasis> Gene in Cultivated Rice and its Wild Relatives

Gelatinization temperature (GT), an important parameter for rice cooking quality, is mainly regulated by the ALK gene encoding starch synthase IIa. Here, we reported the nucleotide diversity of the ALK gene in 122 cultivated accessions and 199 wild rice accessions that were collected around the Pearl River Basin in China. A total of 93 single nucleotide ploymorphisms (SNPs) were identified, with an average of one SNP per 40 bp. Tajima D statistics revealed that the DNA sequences covering the last exon have probably evolved under balancing selection. Based on two functional SNPs (an A to G substitution at 4198 bp and a GC to TT dinucleotide substitution at 4330/4331 bp), three haplotypes, G/GC, G/TT, and A/GC, were identified in both wild and cultivated accessions, with the G/GC haplotype being predominant. Interestingly, the A/GC haplotype was exclusively found in the wild accessions from Guangdong province, while the G/TT haplotype was only present in the wild accessions from Jiangxi province and Hainan Island. This suggests that the G/TT and A/GC variants may have arisen independently and undergone balancing selection on separate haplotypes in multiple populations. Our result supports earlier hypothesis that cultivated rice was independently domesticated from multiple domestication events in China. Our study aids in the understanding of the domestication process that led to the improvement of rice grain quality.     

Spontaneous Mutation at the Mtr Locus in Neurospora: The Molecular Spectrum in Wild-Type and a Mutator Strain

Sequence analysis of 34 mtr mutations has yielded the first molecular spectrum of spontaneous mutants in Neurospora crassa. The great majority of the mutations are base substitutions (48%) or deletions (35%). In addition, sequence analysis of the entire mtr region, including the 1472-base pair open reading frame and 1205 base pairs of flanking DNA, was performed in both the Oak Ridge and Mauriceville strains of Neurospora, which are known to be divergent at the DNA level. Sixteen sequence differences between these two strains have been found in the mtr region, with 13 of these in DNA flanking the open reading frame. The differences consisted of base substitutions and small frameshifts at monotonic runs. This set of sequence differences has allowed a comparison of mutations in unselected DNA to those mutations that produce a phenotypic signal. We have isolated a mutator strain (mut-1) of Neurospora in which the spontaneous mutation rate at various loci is as much as 80-fold higher than in the non-mutator (wild type). Twenty-one mtr mutations in the mutator background have been sequenced and compared to the non-mutator spectrum, revealing a striking increase in -1 frameshift mutations. These frameshifts occur exclusively within or adjacent to monotonic runs and can be explained by small slippage events during DNA replication. This argues for a role of the mut-1 gene in this process.     

Molecular Clocks and Archeogenomics of a Late Period Egyptian Date Palm Leaf Reveal Introgression from Wild Relatives and Add Timestamps on the Domestication

The date palm, Phoenix dactylifera, has been a cornerstone of Middle Eastern and North African agriculture for millennia. It was first domesticated in the Persian Gulf, and its evolution appears to have been influenced by gene flow from two wild relatives, P. theophrasti, currently restricted to Crete and Turkey, and P. sylvestris, widespread from Bangladesh to the West Himalayas. Genomes of ancient date palm seeds show that gene flow from P. theophrasti to P. dactylifera may have occurred by ∼2,200 years ago, but traces of P. sylvestris could not be detected. We here integrate archeogenomics of a ∼2,100-year-old P. dactylifera leaf from Saqqara (Egypt), molecular-clock dating, and coalescence approaches with population genomic tests, to probe the hybridization between the date palm and its two closest relatives and provide minimum and maximum timestamps for its reticulated evolution. The Saqqara date palm shares a close genetic affinity with North African date palm populations, and we find clear genomic admixture from both P. theophrasti, and P. sylvestris, indicating that both had contributed to the date palm genome by 2,100 years ago. Molecular-clocks placed the divergence of P. theophrasti from P. dactylifera/P. sylvestris and that of P. dactylifera from P. sylvestris in the Upper Miocene, but strongly supported, conflicting topologies point to older gene flow between P. theophrasti and P. dactylifera, and P. sylvestris and P. dactylifera. Our work highlights the ancient hybrid origin of the date palms, and prompts the investigation of the functional significance of genetic material introgressed from both close relatives, which in turn could prove useful for modern date palm breeding.     

Molecular Cloning and Analysis of L(1)ogre, a Locus of Drosophila Melanogaster with Prominent Effects on the Postembryonic Development of the Central Nervous System

Previous genetic studies have shown that wild-type function of the l(1)ogre (lethal (1) optic ganglion reduced) locus is essential for the generation and/or maintenance of the postembryonic neuroblasts including those from which the optic lobe is descended. In the present study molecular isolation and characterization of the l(1)ogre locus was carried out to study the structure and expression of this gene in order to gain information about the nature of l(1)ogre function and its relevance to the development of the central nervous system. About 70 kilobases (kb) of genomic DNA were isolated that spanned the region where l(1)ogre was known to reside. Southern analysis of a l(1)ogre mutation and subsequent P element-mediated DNA transformation mapped the l(1)ogre+ function within a genomic fragment of 12.5 kb. Northern analyses showed that a 2.9-kb message transcribed from this 12.5-kb region represented l(1)ogre. A 2.15-kb portion of a corresponding cDNA clone was sequenced. An open reading frame (ORF) of 1,086 base paris was found, and a protein sequence of 362 amino acids with one highly hydrophobic segment was deduced from conceptual translation of this ORF.     

中国田鼠卵巢细胞gpt基因自发和亚砷酸钠诱发突变的分子分析

本文研究了亚砷酸钠对CHO-AS52细胞gpt基因的致突变作用。实验结果表明,亚砷酸钠能诱发该基因发生突变,且其突变频率随砷浓度的增加而增高。PCR分析指出,绝大多数亚砷酸钠诱发的CHO-AS52突变体的gpt基因完全缺失。在CHO-AS52细胞自发的、50μmol/L和100μmol/L亚砷酸钠诱发的突变体中,gpt基因完全缺失者所占比率分别为36.00％、54.72％及66.67％。对亚砷酸钠诱发的非缺失型gpt基因突变的PCR产物直接进行DNA序列分析表明,在9个突变细胞克隆中,有2个发生移码突变,其余7个突变细胞克隆的gpt基因结构未发现改变,碱基的改变可能发生在基因启动子区。