Publications (12)58.67 Total impact
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Article: Generation of a large-scale genomic resource for functional and comparative genomics in Liriodendron tulipifera L.
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ABSTRACT: Liriodendron tulipifera L., a member of Magnoliaceae in the order Magnoliales, has been used extensively as a reference species in studies on plant evolution. However, genomic resources for this tree species are limited. We constructed cDNA libraries from ten different types of tissues: premeiotic flower buds, postmeiotic flower buds, open flowers, developing fruit, terminal buds, leaves, cambium, xylem, roots, and seedlings. EST sequences were generated either by 454 GS FLX or Sanger methods. Assembly of almost 2.4 million sequencing reads from all libraries resulted in 137,923 unigenes (132,905 contigs and 4,599 singletons). About 50% of the unigenes had significant matches to publically available plant protein sequences, representing a wide variety of putative functions. Approximately 30,000 simple sequence repeats were identified. More than 97% of the cell wall formation genes in the Cell Wall Navigator and the MAIZEWALL databases are represented. The cinnamyl alcohol dehydrogenase (CAD) homologs identified in the L. tulipifera EST dataset showed different expression levels in the ten tissue types included in this study. In particular, the LtuCAD1 was found to partially recover the stiffness of the floral stems in the Arabidopsis thaliana CAD4 and CAD5 double mutant plants, of the LtuCAD1 in lignin biosynthesis. L. tulipifera genes have greater sequence similarity to homologs from other woody angiosperm species than to non-woody model plants. This large-scale genomic resour"HistryDatesce will be instrumental for gene discovery, cDNA microarray production, and marker-assisted breeding in L. tulipifera, and strengthen this species' role in comparative studies. KeywordsEST database–Xylogenesis– Liriodendron –Yellow-poplar–MagnoliaceaeTree Genetics & Genomes 04/2012; 7(5):941-954. · 2.34 Impact Factor -
Article: An EST database for Liriodendron tulipifera L. floral buds: the first EST resource for functional and comparative genomics in Liriodendron
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ABSTRACT: Liriodendron tulipifera L. was selected by the Floral Genome Project for identification of new genes related to floral diversity in basal angiosperms. A large, non-normalized cDNA library was constructed from premeiotic and meiotic floral buds and sequenced to generate a database of 9,531 high-quality expressed sequence tags. These sequences clustered into 6,520 unigenes, of which 5,251 were singletons, and 1,269 were in contigs. Homologs of genes regulating many aspects of flower development were identified, including those for organ identity and development, cell and tissue differentiation, and cell-cycle control. Almost 5% of the transcriptome consisted of homologs to known floral gene families. Homologs of most of the genes involved in cell-wall construction were also recovered. This provides a new opportunity for comparative studies in lignin biosynthesis, a trait of key importance in the evolution of land plants and in the utilization of fiber from economically important tree species, such as Liriodendron. Also of note is that 1,089 unigenes did not match any sequence in the public databases, including the complete genomes of Arabidopsis, rice, and Populus. Some of these novel genes might be unique in basal angiosperm species and, when better characterized, may be informative for understanding the origins of diverged gene families. Thus, the Liriodendron expressed sequence tag database and library will help bridge our understanding of the mechanisms of flower initiation and development that are shared among basal angiosperms, eudicots, and monocots, and provide new opportunities for comparative analysis of gene families across angiosperm species.Tree Genetics & Genomes 04/2012; 4(3):419-433. · 2.34 Impact Factor -
Article: Comparative transcriptomics among floral organs of the basal eudicot Eschscholzia californica as reference for floral evolutionary developmental studies.
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ABSTRACT: Molecular genetic studies of floral development have concentrated on several core eudicots and grasses (monocots), which have canalized floral forms. Basal eudicots possess a wider range of floral morphologies than the core eudicots and grasses and can serve as an evolutionary link between core eudicots and monocots, and provide a reference for studies of other basal angiosperms. Recent advances in genomics have enabled researchers to profile gene activities during floral development, primarily in the eudicot Arabidopsis thaliana and the monocots rice and maize. However, our understanding of floral developmental processes among the basal eudicots remains limited. Using a recently generated expressed sequence tag (EST) set, we have designed an oligonucleotide microarray for the basal eudicot Eschscholzia californica (California poppy). We performed microarray experiments with an interwoven-loop design in order to characterize the E. californica floral transcriptome and to identify differentially expressed genes in flower buds with pre-meiotic and meiotic cells, four floral organs at preanthesis stages (sepals, petals, stamens and carpels), developing fruits, and leaves. Our results provide a foundation for comparative gene expression studies between eudicots and basal angiosperms. We identified whorl-specific gene expression patterns in E. californica and examined the floral expression of several gene families. Interestingly, most E. californica homologs of Arabidopsis genes important for flower development, except for genes encoding MADS-box transcription factors, show different expression patterns between the two species. Our comparative transcriptomics study highlights the unique evolutionary position of E. californica compared with basal angiosperms and core eudicots.Genome biology 10/2010; 11(10):R101. · 6.63 Impact Factor -
Article: Positive selection and expression divergence following gene duplication in the sunflower CYCLOIDEA gene family.
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ABSTRACT: Members of the CYCLOIDEA (CYC)/TEOSINTE-BRANCHED1 (TB1) group of transcription factors have been implicated in the evolution of zygomorphic (i.e., bilaterally symmetric) flowers in Antirrhinum and Lotus and the loss of branching phenotype during the domestication of maize. The composite inflorescences of sunflower (Helianthus annuus L. Asteraceae) contain both zygomorphic and actinomorphic (i.e., radially symmetric) florets (rays and disks, respectively), and the cultivated sunflower has evolved an unbranched phenotype in response to domestication from its highly branched wild progenitor; hence, genes related to CYC/TB1 are of great interest in this study system. We identified 10 members of the CYC/TB1 gene family in sunflower, which is more than found in any other species investigated to date. Phylogenetic analysis indicates that these genes occur in 3 distinct clades, consistent with previous research in other eudicot species. A combination of dating the duplication events and linkage mapping indicates that only some of the duplications were associated with polyploidization. Cosegregation between CYC-like genes and branching-related quantitative trait loci suggest a minor, if any, role for these genes in conferring differences in branching. However, the expression patterns of one gene suggest a possible role in the development of ray versus disk florets. Molecular evolutionary analyses reveal that residues in the conserved domains were the targets of positive selection following gene duplication. Taken together, these results indicate that gene duplication and functional divergence have played a major role in diversification of the sunflower CYC gene family.Molecular Biology and Evolution 08/2008; 25(7):1260-73. · 5.55 Impact Factor -
Article: Recharacterization of ancient DNA miscoding lesions: insights in the era of sequencing-by-synthesis.
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ABSTRACT: Although ancient DNA (aDNA) miscoding lesions have been studied since the earliest days of the field, their nature remains a source of debate. A variety of conflicting hypotheses exist about which miscoding lesions constitute true aDNA damage as opposed to PCR polymerase amplification error. Furthermore, considerable disagreement and speculation exists on which specific damage events underlie observed miscoding lesions. The root of the problem is that it has previously been difficult to assemble sufficient data to test the hypotheses, and near-impossible to accurately determine the specific strand of origin of observed damage events. With the advent of emulsion-based clonal amplification (emPCR) and the sequencing-by-synthesis technology this has changed. In this paper we demonstrate how data produced on the Roche GS20 genome sequencer can determine miscoding lesion strands of origin, and subsequently be interpreted to enable characterization of the aDNA damage behind the observed phenotypes. Through comparative analyses on 390,965 bp of modern chloroplast and 131,474 bp of ancient woolly mammoth GS20 sequence data we conclusively demonstrate that in this sample at least, a permafrost preserved specimen, Type 2 (cytosine-->thymine/guanine-->adenine) miscoding lesions represent the overwhelming majority of damage-derived miscoding lesions. Additionally, we show that an as yet unidentified guanine-->adenine analogue modification, not the conventionally argued cytosine-->uracil deamination, underpins a significant proportion of Type 2 damage. How widespread these implications are for aDNA will become apparent as future studies analyse data recovered from a wider range of substrates.Nucleic Acids Research 01/2007; 35(1):1-10. · 8.03 Impact Factor -
Article: EST database for early flower development in California poppy (Eschscholzia californica Cham., Papaveraceae) tags over 6,000 genes from a basal eudicot.
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ABSTRACT: The Floral Genome Project (FGP) selected California poppy (Eschscholzia californica Cham. ssp. Californica) to help identify new florally-expressed genes related to floral diversity in basal eudicots. A large, non-normalized cDNA library was constructed from premeiotic and meiotic floral buds and sequenced to generate a database of 9,079 high quality Expressed Sequence Tags (ESTs). These sequences clustered into 5,713 unigenes, including 1,414 contigs and 4,299 singletons. Homologs of genes regulating many aspects of flower development were identified, including those for organ identity and development, cell and tissue differentiation, cell cycle control, and secondary metabolism. Over 5% of the transcriptome consisted of homologs to known floral gene families. Most are the first representatives of their respective gene families in basal eudicots and their conservation suggests they are important for floral development and/or function. App. 10% of the transcripts encoded transcription factors and other regulatory genes, including nine genes from the seven major lineages of the important MADS-box family of developmental regulators. Homologs of alkaloid pathway genes were also recovered, providing opportunities to explore adaptive evolution in secondary products. Furthermore, comparison of the poppy ESTs with the Arabidopsis genome provided support for putative Arabidopsis genes that previously lacked annotation. Finally, over 1,800 unique sequences had no observable homology in the public databases. The California poppy EST database and library will help bridge our understanding of flower initiation and development among higher eudicot and monocot model plants and provide new opportunities for comparative analysis of gene families across angiosperm species.Plant Molecular Biology 11/2006; 62(3):351-69. · 4.15 Impact Factor -
Article: Using partial genomic fosmid libraries for sequencing complete organellar genomes.
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ABSTRACT: Organellar genome sequences provide numerous phylogenetic markers and yield insight into organellar function and molecular evolution. These genomes are much smaller in size than their nuclear counterparts; thus, their complete sequencing is much less expensive than total nuclear genome sequencing, making broader phylogenetic sampling feasible. However; for some organisms, it is challenging to isolate plastid DNA for sequencing using standard methods. To overcome these difficulties, we constructed partial genomic libraries from total DNA preparations of two heterotrophic and two autotrophic angiosperm species using fosmid vectors. We then used macroarray screening to isolate clones containing large fragments of plastid DNA. A minimum tiling path of clones comprising the entire genome sequence of each plastid was selected, and these clones were shotgun-sequenced and assembled into complete genomes. Although this method worked well for both heterotrophic and autotrophic plants, nuclear genome size had a dramatic effect on the proportion of screened clones containing plastid DNA and, consequently, the overall number of clones that must be screened to ensure full plastid genome coverage. This technique makes it possible to determine complete plastid genome sequences for organisms that defy other available organellar genome sequencing methods, especially those for which limited amounts of tissue are available.BioTechniques 08/2006; 41(1):69-73. · 2.67 Impact Factor -
Article: Widespread genome duplications throughout the history of flowering plants.
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ABSTRACT: Genomic comparisons provide evidence for ancient genome-wide duplications in a diverse array of animals and plants. We developed a birth-death model to identify evidence for genome duplication in EST data, and applied a mixture model to estimate the age distribution of paralogous pairs identified in EST sets for species representing the basal-most extant flowering plant lineages. We found evidence for episodes of ancient genome-wide duplications in the basal angiosperm lineages including Nuphar advena (yellow water lily: Nymphaeaceae) and the magnoliids Persea americana (avocado: Lauraceae), Liriodendron tulipifera (tulip poplar: Magnoliaceae), and Saruma henryi (Aristolochiaceae). In addition, we detected independent genome duplications in the basal eudicot Eschscholzia californica (California poppy: Papaveraceae) and the basal monocot Acorus americanus (Acoraceae), both of which were distinct from duplications documented for ancestral grass (Poaceae) and core eudicot lineages. Among gymnosperms, we found equivocal evidence for ancient polyploidy in Welwitschia mirabilis (Gnetales) and no evidence for polyploidy in pine, although gymnosperms generally have much larger genomes than the angiosperms investigated. Cross-species sequence divergence estimates suggest that synonymous substitution rates in the basal angiosperms are less than half those previously reported for core eudicots and members of Poaceae. These lower substitution rates permit inference of older duplication events. We hypothesize that evidence of an ancient duplication observed in the Nuphar data may represent a genome duplication in the common ancestor of all or most extant angiosperms, except Amborella.Genome Research 07/2006; 16(6):738-49. · 13.61 Impact Factor -
Article: An expressed sequence tag (EST) library from developing fruits of an Hawaiian endemic mint (Stenogyne rugosa, Lamiaceae): characterization and microsatellite markers.
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ABSTRACT: The endemic Hawaiian mints represent a major island radiation that likely originated from hybridization between two North American polyploid lineages. In contrast with the extensive morphological and ecological diversity among taxa, ribosomal DNA sequence variation has been found to be remarkably low. In the past few years, expressed sequence tag (EST) projects on plant species have generated a vast amount of publicly available sequence data that can be mined for simple sequence repeats (SSRs). However, these EST projects have largely focused on crop or otherwise economically important plants, and so far only few studies have been published on the use of intragenic SSRs in natural plant populations. We constructed an EST library from developing fleshy nutlets of Stenogyne rugosa principally to identify genetic markers for the Hawaiian endemic mints. The Stenogyne fruit EST library consisted of 628 unique transcripts derived from 942 high quality ESTs, with 68% of unigenes matching Arabidopsis genes. Relative frequencies of Gene Ontology functional categories were broadly representative of the Arabidopsis proteome. Many unigenes were identified as putative homologs of genes that are active during plant reproductive development. A comparison between unigenes from Stenogyne and tomato (both asterid angiosperms) revealed many homologs that may be relevant for fruit development. Among the 628 unigenes, a total of 44 potentially useful microsatellite loci were predicted. Several of these were successfully tested for cross-transferability to other Hawaiian mint species, and at least five of these demonstrated interesting patterns of polymorphism across a large sample of Hawaiian mints as well as close North American relatives in the genus Stachys. Analysis of this relatively small EST library illustrated a broad GO functional representation. Many unigenes could be annotated to involvement in reproductive development. Furthermore, first tests of microsatellite primer pairs have proven promising for the use of Stenogyne rugosa EST SSRs for evolutionary and phylogeographic studies of the Hawaiian endemic mints and their close relatives. Given that allelic repeat length variation in developmental genes of other organisms has been linked with morphological evolution, these SSRs may also prove useful for analyses of phenotypic differences among Hawaiian mints.BMC Plant Biology 02/2006; 6:16. · 3.45 Impact Factor -
Article: The evolution of the SEPALLATA subfamily of MADS-box genes: a preangiosperm origin with multiple duplications throughout angiosperm history.
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ABSTRACT: Members of the SEPALLATA (SEP) MADS-box subfamily are required for specifying the "floral state" by contributing to floral organ and meristem identity. SEP genes have not been detected in gymnosperms and seem to have originated since the lineage leading to extant angiosperms diverged from extant gymnosperms. Therefore, both functional and evolutionary studies suggest that SEP genes may have been critical for the origin of the flower. To gain insights into the evolution of SEP genes, we isolated nine genes from plants that occupy phylogenetically important positions. Phylogenetic analyses of SEP sequences show that several gene duplications occurred during the evolution of this subfamily, providing potential opportunities for functional divergence. The first duplication occurred prior to the origin of the extant angiosperms, resulting in the AGL2/3/4 and AGL9 clades. Subsequent duplications occurred within these clades in the eudicots and monocots. The timing of the first SEP duplication approximately coincides with duplications in the DEFICIENS/GLOBOSA and AGAMOUS MADS-box subfamilies, which may have resulted from either a proposed genome-wide duplication in the ancestor of extant angiosperms or multiple independent duplication events. Regardless of the mechanism of gene duplication, these pairs of duplicate transcription factors provided new possibilities of genetic interactions that may have been important in the origin of the flower.Genetics 05/2005; 169(4):2209-23. · 4.01 Impact Factor -
Article: Floral gene resources from basal angiosperms for comparative genomics research.
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ABSTRACT: The Floral Genome Project was initiated to bridge the genomic gap between the most broadly studied plant model systems. Arabidopsis and rice, although now completely sequenced and under intensive comparative genomic investigation, are separated by at least 125 million years of evolutionary time, and cannot in isolation provide a comprehensive perspective on structural and functional aspects of flowering plant genome dynamics. Here we discuss new genomic resources available to the scientific community, comprising cDNA libraries and Expressed Sequence Tag (EST) sequences for a suite of phylogenetically basal angiosperms specifically selected to bridge the evolutionary gaps between model plants and provide insights into gene content and genome structure in the earliest flowering plants. Random sequencing of cDNAs from representatives of phylogenetically important eudicot, non-grass monocot, and gymnosperm lineages has so far (as of 12/1/04) generated 70,514 ESTs and 48,170 assembled unigenes. Efficient sorting of EST sequences into putative gene families based on whole Arabidopsis/rice proteome comparison has permitted ready identification of cDNA clones for finished sequencing. Preliminarily, (i) proportions of functional categories among sequenced floral genes seem representative of the entire Arabidopsis transcriptome, (ii) many known floral gene homologues have been captured, and (iii) phylogenetic analyses of ESTs are providing new insights into the process of gene family evolution in relation to the origin and diversification of the angiosperms. Initial comparisons illustrate the utility of the EST data sets toward discovery of the basic floral transcriptome. These first findings also afford the opportunity to address a number of conspicuous evolutionary genomic questions, including reproductive organ transcriptome overlap between angiosperms and gymnosperms, genome-wide duplication history, lineage-specific gene duplication and functional divergence, and analyses of adaptive molecular evolution. Since not all genes in the floral transcriptome will be associated with flowering, these EST resources will also be of interest to plant scientists working on other functions, such as photosynthesis, signal transduction, and metabolic pathways.BMC Plant Biology 02/2005; 5:5. · 3.45 Impact Factor -
Article: Conservation and divergence in the AGAMOUS subfamily of MADS-box genes: evidence of independent sub- and neofunctionalization events.
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ABSTRACT: The MADS-box gene AGAMOUS (AG) plays a key role in determining floral meristem and organ identities. We identified three AG homologs, EScaAG1, EScaAG2, and EScaAGL11 from the basal eudicot Eschscholzia californica (California poppy). Phylogenetic analyses indicate that EScaAG1 and EScaAG2 are recent paralogs within the AG clade, independent of the duplication in ancestral core eudicots that gave rise to the euAG and PLENA (PLE) orthologs. EScaAGL11 is basal to core eudicot AGL11 orthologs in a clade representing an older duplication event after the divergence of the angiosperm and gymnosperm lineages. Detailed in situ hybridization experiments show that expression of EScaAG1 and EScaAG2 is similar to AG; however, both genes appear to be expressed earlier in floral development than described in the core eudicots. A thorough examination of available expression and functional data in a phylogenetic context for members of the AG and AGL11 clades reveals that gene expression has been quite variable throughout the evolutionary history of the AG subfamily and that ovule-specific expression might have evolved more than twice. Although sub- and neofunctionalization are inferred to have occurred following gene duplication, functional divergence among orthologs is evident, as is convergence, among paralogs sampled from different species. We propose that retention of multiple AG homologs in several paralogous lineages can be explained by the conservation of ancestral protein activity combined with evolutionarily labile regulation of expression in the AG and AGL11 clades such that the collective functions of the AG subfamily in stamen and carpel development are maintained following gene duplication.Evolution & Development 8(1):30-45. · 2.47 Impact Factor
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- BMC Plant Biology (2)
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Institutions
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2012
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Fudan University
Shanghai, Shanghai Shi, China -
Clemson University
Anderson, IN, USA -
University of Georgia
- Department of Plant Biology
Athens, GA, USA
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2005–2010
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Pennsylvania State University
- Department of Biology
University Park, MD, USA -
University of Oslo
Oslo, Oslo, Norway
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