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Susan McCouch

Publications and source records attributed to Susan McCouch.

11 recordsLinked to original sources
PubMed2006

Whole-plant growth stage ontology for angiosperms and its application in plant biology.

Plant growth stages are identified as distinct morphological landmarks in a continuous developmental process. The terms describing these developmental stages record the morphological appearance of the plant at a specific point in its life cycle. The widely differing morphology of plant species consequently gave rise to heterogeneous vocabularies describing growth and development. Each species or family specific community developed distinct terminologies for describing whole-plant growth stages. This semantic heterogeneity made it impossible to use growth stage description contained within plant biology databases to make meaningful computational comparisons. The Plant Ontology Consortium (http://www.plantontology.org) was founded to develop standard ontologies describing plant anatomical as well as growth and developmental stages that can be used for annotation of gene expression patterns and phenotypes of all flowering plants. In this article, we describe the development of a generic whole-plant growth stage ontology that describes the spatiotemporal stages of plant growth as a set of landmark events that progress from germination to senescence. This ontology represents a synthesis and integration of terms and concepts from a variety of species-specific vocabularies previously used for describing phenotypes and genomic information. It provides a common platform for annotating gene function and gene expression in relation to the developmental trajectory of a plant described at the organismal level. As proof of concept the Plant Ontology Consortium used the plant ontology growth stage ontology to annotate genes and phenotypes in plants with initial emphasis on those represented in The Arabidopsis Information Resource, Gramene database, and MaizeGDB.

Arabidopsis↗
PubMed2006

Selection under domestication: evidence for a sweep in the rice waxy genomic region.

Rice (Oryza sativa) was cultivated by Asian Neolithic farmers >11,000 years ago, and different cultures have selected for divergent starch qualities in the rice grain during and after the domestication process. An intron 1 splice donor site mutation of the Waxy gene is responsible for the absence of amylose in glutinous rice varieties. This mutation appears to have also played an important role in the origin of low amylose, nonglutinous temperate japonica rice varieties, which form a primary component of Northeast Asian cuisines. Waxy DNA sequence analyses indicate that the splice donor mutation is prevalent in temperate japonica rice varieties, but rare or absent in tropical japonica, indica, aus, and aromatic varieties. Sequence analysis across a 500-kb genomic region centered on Waxy reveals patterns consistent with a selective sweep in the temperate japonicas associated with the mutation. The size of the selective sweep (>250 kb) indicates very strong selection in this region, with an inferred selection coefficient that is higher than similar estimates from maize domestication genes or wild species. These findings demonstrate that selection pressures associated with crop domestication regimes can exceed by one to two orders of magnitude those observed for genes under even strong selection in natural systems.

Agriculture↗
PubMed2006

Caught red-handed: Rc encodes a basic helix-loop-helix protein conditioning red pericarp in rice.

Rc is a domestication-related gene required for red pericarp in rice (Oryza sativa). The red grain color is ubiquitous among the wild ancestors of O. sativa, in which it is closely associated with seed shattering and dormancy. Rc encodes a basic helix-loop-helix (bHLH) protein that was fine-mapped to an 18.5-kb region on rice chromosome 7 using a cross between Oryza rufipogon (red pericarp) and O. sativa cv Jefferson (white pericarp). Sequencing of the alleles from both mapping parents as well as from two independent genetic stocks of Rc revealed that the dominant red allele differed from the recessive white allele by a 14-bp deletion within exon 6 that knocked out the bHLH domain of the protein. A premature stop codon was identified in the second mutant stock that had a light red pericarp. RT-PCR experiments confirmed that the Rc gene was expressed in both red- and white-grained rice but that a shortened transcript was present in white varieties. Phylogenetic analysis, supported by comparative mapping in rice and maize (Zea mays), showed that Rc, a positive regulator of proanthocyanidin, is orthologous with INTENSIFIER1, a negative regulator of anthocyanin production in maize, and is not in the same clade as rice bHLH anthocyanin regulators.

Amino Acid Sequence↗
PubMed2006

Gramene: a bird's eye view of cereal genomes.

Rice, maize, sorghum, wheat, barley and the other major crop grasses from the family Poaceae (Gramineae) are mankind's most important source of calories and contribute tens of billions of dollars annually to the world economy (FAO 1999, http://www.fao.org; USDA 1997, http://www.usda.gov). Continued improvement of Poaceae crops is necessary in order to continue to feed an ever-growing world population. However, of the major crop grasses, only rice (Oryza sativa), with a compact genome of approximately 400 Mbp, has been sequenced and annotated. The Gramene database (http://www.gramene.org) takes advantage of the known genetic colinearity (synteny) between rice and the major crop plant genomes to provide maize, sorghum, millet, wheat, oat and barley researchers with the benefits of an annotated genome years before their own species are sequenced. Gramene is a one stop portal for finding curated literature, genetic and genomic datasets related to maps, markers, genes, genomes and quantitative trait loci. The addition of several new tools to Gramene has greatly facilitated the potential for comparative analysis among the grasses and contributes to our understanding of the anatomy, development, environmental responses and the factors influencing agronomic performance of cereal crops. Since the last publication on Gramene database by D. H. Ware, P. Jaiswal, J. Ni, I. V. Yap, X. Pan, K. Y. Clark, L. Teytelman, S. C. Schmidt, W. Zhao, K. Chang et al. [(2002), Plant Physiol., 130, 1606-1613], the database has undergone extensive changes that are described in this publication.

Arabidopsis↗
PubMed2005

The Oryza bacterial artificial chromosome library resource: construction and analysis of 12 deep-coverage large-insert BAC libraries that represent the 10 genome types of the genus Oryza.

Rice (Oryza sativa L.) is the most important food crop in the world and a model system for plant biology. With the completion of a finished genome sequence we must now functionally characterize the rice genome by a variety of methods, including comparative genomic analysis between cereal species and within the genus Oryza. Oryza contains two cultivated and 22 wild species that represent 10 distinct genome types. The wild species contain an essentially untapped reservoir of agriculturally important genes that must be harnessed if we are to maintain a safe and secure food supply for the 21st century. As a first step to functionally characterize the rice genome from a comparative standpoint, we report the construction and analysis of a comprehensive set of 12 BAC libraries that represent the 10 genome types of Oryza. To estimate the number of clones required to generate 10 genome equivalent BAC libraries we determined the genome sizes of nine of the 12 species using flow cytometry. Each library represents a minimum of 10 genome equivalents, has an average insert size range between 123 and 161 kb, an average organellar content of 0.4%-4.1% and nonrecombinant content between 0% and 5%. Genome coverage was estimated mathematically and empirically by hybridization and extensive contig and BAC end sequence analysis. A preliminary analysis of BAC end sequences of clones from these libraries indicated that LTR retrotransposons are the predominant class of repeat elements in Oryza and a roughly linear relationship of these elements with genome size was observed.

Base Sequence↗
PubMed2005

Genetic structure and diversity in Oryza sativa L.

The population structure of domesticated species is influenced by the natural history of the populations of predomesticated ancestors, as well as by the breeding system and complexity of the breeding practices exercised by humans. Within Oryza sativa, there is an ancient and well-established divergence between the two major subspecies, indica and japonica, but finer levels of genetic structure are suggested by the breeding history. In this study, a sample of 234 accessions of rice was genotyped at 169 nuclear SSRs and two chloroplast loci. The data were analyzed to resolve the genetic structure and to interpret the evolutionary relationships between groups. Five distinct groups were detected, corresponding to indica, aus, aromatic, temperate japonica, and tropical japonica rices. Nuclear and chloroplast data support a closer evolutionary relationship between the indica and the aus and among the tropical japonica, temperate japonica, and aromatic groups. Group differences can be explained through contrasting demographic histories. With the availability of rice genome sequence, coupled with a large collection of publicly available genetic resources, it is of interest to develop a population-based framework for the molecular analysis of diversity in O. sativa.

Base Sequence↗
PubMed2004

Simple sequence repeat diversity in diploid and tetraploid Coffea species.

Thirty-four fluorescently labeled microsatellite markers were used to assess genetic diversity in a set of 30 Coffea accessions from the CENICAFE germplasm bank in Colombia. The plant material included one sample per accession of seven East African accessions representing five diploid species and 23 wild and cultivated tetraploid accessions of Coffea arabica from Africa, Indonesia, and South America. More allelic diversity was detected among the five diploid species than among the 23 tetraploid genotypes. The diploid species averaged 3.6 alleles/locus and had an average polymorphism information content (PIC) value of 0.6, whereas the wild tetraploids averaged 2.5 alleles/locus and had an average PIC value of 0.3 and the cultivated tetraploids (C. arabica cultivars) averaged 1.9 alleles/locus and had an average PIC value of 0.22. Fifty-five percent of the alleles found in the wild tetraploids were not shared with cultivated C. arabica genotypes, supporting the idea that the wild tetraploid ancestors from Ethiopia could be used productively as a source of novel genetic variation to expand the gene pool of elite C. arabica germplasm.

Base Sequence↗
PubMed2002

Gramene: a resource for comparative grass genomics.

Gramene (http://www.gramene.org) is a comparative genome mapping database for grasses and a community resource for rice. Rice, in addition to being an economically important crop, is also a model monocot for understanding other agronomically important grass genomes. Gramene replaces the existing AceDB database 'RiceGenes' with a relational database based on Oracle. Gramene provides curated and integrative information about maps, sequence, genes, genetic markers, mutants, QTLs, controlled vocabularies and publications. Its aims are to use the rice genetic, physical and sequence maps as fundamental organizing units, to provide a common denominator for moving from one crop grass to another and is to serve as a portal for interconnecting with other web-based crop grass resources. This paper describes the initial steps we have taken towards realizing these goals.

Chromosome Mapping↗
PubMed2002

Constructing comparative genome maps with unresolved marker order.

Comparative genome maps are a powerful tool for interpreting the genomes of related organisms. The species maps which are the input to the process of constructing comparative maps are often themselves constructed from incomplete or inconsistent data, resulting in markers (or genes) whose order is not fully resolved. This incomplete marker order information is often handled by placing markers whose relative order cannot be reliably inferred together in a bin which is mapped to a common location. Previous automated and manual methods have handled such markers in an ad hoc or arbitrary way. We present efficient algorithms for comparative map construction that provide a principled method for handling unresolved marker order. The algorithms are based on a technique for efficiently computing a marker order that optimizes a natural parsimony criterion; in this way, they also yield a working hypothesis about the original incomplete data set.

Algorithms↗