不受欢迎的生物多样性：香港的外来植物物种

香港早在19世纪中叶开始就有外来植物入侵的记录,迄今为止,已发现多达238种已归化的外来或怀疑为外来的植物,其中又以薇甘菊（Mikania micrantha)、五爪金龙（Ipomoea cairica)、假臭草（Eupatorium catarium)、大黍（Panicum maximum)等最常见,外来植物最常见于受人为干扰的生境,例如荒废农田及路旁等,而较少在天然林地生境及贫瘠的灌草丛中发现,外来植物的对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少了生境及贫瘠的灌草丛中发现,外来植物对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少少了生境及动植物的多样性,外来动物对香港原生植物影响最大的是于20世纪70年代入侵的松树线虫（Bur-saphelenchus xylophilus)。外来的脊椎动物也有可能对香港的植物被演替产生影响,目前香港的外来植物当中,有些在大陆较少分布或没有记录,作为华南最大的港口,香港对外来物种的引入扮演着重要的角色,因此制定控制外来种在香港及华南地区的引入及传播的政策及措施非常重要。     

Identification,analysis, and utilization of conserved ortholog set markers for comparative genomics in higher plants

We have screened a large tomato EST database against the Arabidopsis genomic sequence and report here the identification of a set of 1025 genes (referred to as a conserved ortholog set, or COS markers) that are single or low copy in both genomes (as determined by computational screens and DNA gel blot hybridization) and that have remained relatively stable in sequence since the early radiation of dicotyledonous plants. These genes were annotated, and a large portion could be assigned to putative functional categories associated with basic metabolic processes, such as energy-generating processes and the biosynthesis and degradation of cellular building blocks. We further demonstrate, through computational screens (e.g., against a Medicago truncatula database) and direct hybridization on genomic DNA of diverse plant species, that these COS markers also are conserved in the genomes of other plant families. Finally, we show that this gene set can be used for comparative mapping studies between highly divergent genomes such as those of tomato and Arabidopsis. This set of COS markers, identified computationally and experimentally, may further studies on comparative genomes and phylogenetics and elucidate the nature of genes conserved throughout plant evolution.     

COSII genetic maps of two diploid Nicotiana species provide a detailed picture of synteny with tomato and insights into chromosome evolution in tetraploid N. tabacum

Using single-copy conserved ortholog set (COSII) and simple sequence repeat (SSR) markers, we have constructed two genetic maps for diploid Nicotiana species, N. tomentosiformis and N. acuminata, respectively. N. acuminata is phylogenetically closer to N. sylvestris than to N. tomentosiformis, the latter two of which are thought to contribute the S-genome and T-genome, respectively, to the allotetraploid tobacco (N. tabacum L., 2n = 48). A comparison of the two maps revealed a minimum of seven inversions and one translocation subsequent to the divergence of these two diploid species. Further, comparing the diploid maps with a dense tobacco map revealed that the tobacco genome experienced chromosomal rearrangements more frequently than its diploid relatives, supporting the notion of accelerated genome evolution in allotetraploids. Mapped COSII markers permitted the investigation of Nicotiana–tomato syntenic relationships. A minimum of 3 (and up to 10) inversions and 11 reciprocal translocations differentiate the tomato genome from that of the last common ancestor of N. tomentosiformis and N. acuminata. Nevertheless, the marker/gene order is well preserved in 25 conserved syntenic segments. Molecular dating based on COSII sequences suggested that tobacco was formed 1.0MYA or later. In conclusion, these COSII and SSR markers link the cultivated tobacco map to those of wild diploid Nicotiana species and tomato, thus providing a platform for cross-reference of genetic and genomic information among them as well as other solanaceous species including potato, eggplant, pepper and the closely allied coffee (Rubiaceae). Therefore they will facilitate genetic research in the genus Nicotiana.     

Purification and Characterization of Polyphenol Oxidase from Glandular Trichomes of Solanum berthaultii

Type A glandular trichomes of the wild potato (Solanum berthaultii Hawkes) entrap insects by rapidly polymerizing the trichome contents after breakage by insect contact. Polymerization of trichome exudate appears to be driven by a soluble polyphenol oxidase (PPO). PPO constitutes up to 70% of the protein in individually collected trichomes and reaches a concentration approaching 200 μm in these organs. Trichome PPO has been purified and shown to be a monomeric copper metalloprotein with an isoelectric point of 5.5, possessing only o-diphenol oxygen oxido-reductase activity, and is larger than most other reported PPOs, with relative molecular weight of 59,000. Chlorogenic and caffeic acid were the most readily oxidized of 14 phenolic substrates tested. Polyclonal antibodies raised against the relative molecular weight 59,000 S. berthaultii trichome PPO were used to show that S. tuberosum L. trichomes express low levels of a cross-reactive protein that lacks detectable PPO activity.     

Candidate gene analysis of anthocyanin pigmentation loci in the<Emphasis Type="Italic"> Solanaceae</Emphasis>

Crop species in the Solanaceae, which includes tomato (Lycopersicon esculentum), potato (Solanum tuberosum), pepper (Capsicum spp.), and eggplant (S. melongena), exhibit natural variation in the types, levels, and tissue-specific expression patterns of anthocyanin pigments. While the identities of the genes underpinning natural variation in anthocyanin traits in these crops are largely unknown, many structural genes and regulators of anthocyanin biosynthesis have been isolated from the solanaceous ornamental species Petunia. To identify candidate genes that may correspond to loci controlling natural variation in the four crops, 13 anthocyanin-related genes were localized on a tomato F₂ genetic map. Gene map positions were then compared to mapped mutants in tomato and through comparative genetic maps to natural variants in potato, eggplant, and pepper. Similar map positions suggest that the tomato mutants anthocyaninless, entirely anthocyaninless, and anthocyanin gainer correspond to flavonoid 35-hydroxylase (f35h), anthocyanidin synthase, and the Petunia Myb domain trancriptional regulatory gene an2, respectively. Similarly potato R, required for the production of red pelargonidin-based pigments, P, required for production of purple delphinidin-based pigments, and I, required for tissue-specific expression in tuber skin, appear to correspond to dihydroflavonol 4-reductase, f35h and an2, respectively. The map location of an2 also overlaps pepper A and eggplant fap10.1, lla10.1, lra10.1, sa10.1, pa10.1 and ca10.1, suggesting that a homologous regulatory locus has been subjected to parallel selection in the domestication of many solanaceous crops. To test the hypothesis that tomato anthocyaninless corresponds to f35h, a portion of the gene was sequenced. A premature stop codon was observed in an anthocyaninless mutant, but not in wild-type.Communicated by H.F. Linskens     

A detailed synteny map of the eggplant genome based on conserved ortholog set II (COSII) markers

We report herein the mapping of 115 PCR-based orthologous markers, including 110 conserved ortholog set or COSII markers, on the reference RFLP map of eggplant. The result permitted inference of a detailed syntenic relationship between the eggplant and tomato genomes. Further, the position of additional 522 COSII markers was inferred in the eggplant map via eggplant-tomato synteny, bringing the total number of markers in the eggplant genome to 869. Since divergence from their last common ancestor approximately 12 million years ago, the eggplant and tomato genomes have become differentiated by a minimum number of 24 inversions and 5 chromosomal translocations, as well as a number of single gene transpositions possibly triggered by transposable elements. Nevertheless, the two genomes share 37 conserved syntenic segments (CSSs) within which gene/marker order is well preserved. The high-resolution COSII synteny map described herein provides a platform for cross-reference of genetic and genomic information (including the tomato genome sequence) between eggplant and tomato and therefore will facilitate both applied and basic research in eggplant. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nucleotide polymorphism in the acidic chitinase locus (ChiA) region of the wild plant Arabidopsis thaliana

To investigate DNA variation in natural plant populations, a 1.8-kb region of the acidic chitinase locus (ChiA)was analyzed for 17 ecotypes of Arabidopsis thaliana sampled worldwide and 3 Arabis species in Japan. As in the Adh region, dimorphism was detected throughout the investigated ChiA region, suggesting the possibility that dimorphic DNA variation exists in the entire nuclear genome of A. thaliana. The ChiA region was divided into two blocks by an intragenic recombination between two parental sequence types, which diverged 7.4 MYA under the assumption that nucleotide mutation rate per site per year is mu = 10(- 9). Nucleotide diversity in the entire ChiA region was 0.0104. Tajima's test was significantly negative for both nucleotide and indel variations, which was manifested as an excess of unique polymorphisms. However, the level and pattern of polymorphism in the ChiA region were inconsistent with simple theoretical explanations. The HKA test detected no difference in the levels of intra- and interspecific variations between the ChiA and Adh regions. In the ChiA coding region, no difference in the patterns of synonymous and replacement variation was found in intra- and interspecific comparisons by the MK test. Although it was difficult to determine the exact genetic mechanism acting on the ChA locus, these results suggested that the ChA locus region was under the same genetic mechanism before and after the establishment of A. thaliana as a species.      

Development and application of a suite of non-pungency markers for the Pun1 gene in pepper (Capsicum spp.)

Pungency in peppers is due to the presence of capsaicinoid molecules, which are only produced in Capsicum species. The major gene Pun1 is required for the production of capsaicinoids. Three distinct mutant alleles of Pun1 have been found in three cultivated Capsicum species, one of which has been widely utilized by breeders. Although these mutations have been previously identified, a robust collection of molecular markers for the set of alleles is not available. This has been hindered by the existence of at least one paralogous locus that tends to amplify with Pun1. We present a suite of markers that can differentiate the four Pun1 alleles and test them on a diverse panel of pepper lines and in an F2 population segregating for pungency. These markers will be useful for pepper breeding, germplasm characterization, and seed purity testing.