PubMed Health⌕ Search

Biomedical subjects

R Martienssen

Publications and source records attributed to R Martienssen.

At least 19 recordsLinked to original sources
PubMed2002

The homeobox gene BREVIPEDICELLUS is a key regulator of inflorescence architecture in Arabidopsis.

Flowering plants display a remarkable range of inflorescence architecture, and pedicel characteristics are one of the key contributors to this diversity. However, very little is known about the genes or the pathways that regulate pedicel development. The brevipedicellus (bp) mutant of Arabidopsis thaliana displays a unique phenotype with defects in pedicel development causing downward-pointing flowers and a compact inflorescence architecture. Cloning and molecular analysis of two independent mutant alleles revealed that BP encodes the homeodomain protein KNAT1, a member of the KNOX family. bp-1 is a null allele with deletion of the entire locus, whereas bp-2 has a point mutation that is predicted to result in a truncated protein. In both bp alleles, the pedicels and internodes were compact because of fewer cell divisions; in addition, defects in epidermal and cortical cell differentiation and elongation were found in the affected regions. The downward-pointing pedicels were produced by an asymmetric effect of the bp mutation on the abaxial vs. adaxial sides. Cell differentiation, elongation, and growth were affected more severely on the abaxial than adaxial side, causing the change in the pedicel growth angle. In addition, bp plants displayed defects in cell differentiation and radial growth of the style. Our results show that BP plays a key regulatory role in defining important aspects of the growth and cell differentiation of the inflorescence stem, pedicel, and style in Arabidopsis.

Amino Acid Sequence↗
PubMed2001

Development of leaf shape.

Variation among vascular plants in the initiation and patterning of leaves results in a diverse array of leaf shape, including the strap-like leaf of many grasses and the broad lamina of most eudicots. Recent findings highlight the importance of interactions between the shoot apical meristem (SAM) and developing leaf primordia in axis specification and the establishment of leaf shape. Global regulators of epigenetic states have been implicated in these interactions and may play a role in distinguishing founder cells and stem cells within the SAM.

Genes, Plant↗
PubMed2001

Arabidopsis genes essential for seedling viability: isolation of insertional mutants and molecular cloning.

We have undertaken a large-scale genetic screen to identify genes with a seedling-lethal mutant phenotype. From screening approximately 38,000 insertional mutant lines, we identified >500 seedling-lethal mutants, completed cosegregation analysis of the insertion and the lethal phenotype for >200 mutants, molecularly characterized 54 mutants, and provided a detailed description for 22 of them. Most of the seedling-lethal mutants seem to affect chloroplast function because they display altered pigmentation and affect genes encoding proteins predicted to have chloroplast localization. Although a high level of functional redundancy in Arabidopsis might be expected because 65% of genes are members of gene families, we found that 41% of the essential genes found in this study are members of Arabidopsis gene families. In addition, we isolated several interesting classes of mutants and genes. We found three mutants in the recently discovered nonmevalonate isoprenoid biosynthetic pathway and mutants disrupting genes similar to Tic40 and tatC, which are likely to be involved in chloroplast protein translocation. Finally, we directly compared T-DNA and Ac/Ds transposon mutagenesis methods in Arabidopsis on a genome scale. In each population, we found only about one-third of the insertion mutations cosegregated with a mutant phenotype.

Arabidopsis↗
PubMed2000

Arabidopsis map kinase 4 negatively regulates systemic acquired resistance.

Transposon inactivation of Arabidopsis MAP kinase 4 produced the mpk4 mutant exhibiting constitutive systemic acquired resistance (SAR) including elevated salicylic acid (SA) levels, increased resistance to virulent pathogens, and constitutive pathogenesis-related gene expression shown by Northern and microarray hybridizations. MPK4 kinase activity is required to repress SAR, as an inactive MPK4 form failed to complement mpk4. Analysis of mpk4 expressing the SA hydroxylase NahG and of mpk4/npr1 double mutants indicated that SAR expression in mpk4 is dependent upon elevated SA levels but is independent of NPR1. PDF1.2 and THI2.1 gene induction by jasmonate was blocked in mpk4 expressing NahG, suggesting that MPK4 is required for jasmonic acid-responsive gene expression.

Alleles↗
PubMed2000

Sequence and analysis of chromosome 5 of the plant Arabidopsis thaliana.

The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.

Animals↗
PubMed2000

Redundant regulation of meristem identity and plant architecture by FRUITFULL, APETALA1 and CAULIFLOWER.

The transition from vegetative to reproductive phases during Arabidopsis development is the result of a complex interaction of environmental and endogenous factors. One of the key regulators of this transition is LEAFY (LFY), whose threshold levels of activity are proposed to mediate the initiation of flowers. The closely related APETALA1 (AP1) and CAULIFLOWER (CAL) meristem identity genes are also important for flower initiation, in part because of their roles in upregulating LFY expression. We have found that mutations in the FRUITFULL (FUL) MADS-box gene, when combined with mutations in AP1 and CAL, lead to a dramatic non-flowering phenotype in which plants continuously elaborate leafy shoots in place of flowers. We demonstrate that this phenotype is caused both by the lack of LFY upregulation and by the ectopic expression of the TERMINAL FLOWER1 (TFL1) gene. Our results suggest that the FUL, AP1 and CAL genes act redundantly to control inflorescence architecture by affecting the domains of LFY and TFL1 expression as well as the relative levels of their activities.

Arabidopsis↗
PubMed1999

Clearing a path through the jungle: progress in Arabidopsis genomics.

Progress in sequencing the genome of the model plant Arabidopsis is reviewed. The resulting analysis of the sequence indicates an information-rich genome that is being tackled by a variety of high-throughput approaches aimed at understanding the functions of plant genes. The information derived from these systematic studies is providing important new knowledge of biological processes found uniquely in plants for comparison with that obtained in other multicellular organisms.

Arabidopsis↗
PubMed1999

Copying out our ABCs: the role of gene redundancy in interpreting genetic hierarchies.

The complete sequence of the Arabidopsis genome is scheduled to be determined by the end of the year 2000. While this goal could prove to be something of a moving target (the estimated size of the genome has grown from 120 Mb to 130 Mb over the last year1), it is clear that the majority of genes required for higher plant growth, reproduction and development will have been described within this time frame. Some of the implications of this landmark achievement are already becoming clear, even though less than a half of the genome has been sequenced.

Arabidopsis↗
PubMed1999

zA map for sequence analysis of the Arabidopsis thaliana genome.

Arabidopsis thaliana has emerged as a model system for studies of plant genetics and development, and its genome has been targeted for sequencing by an international consortium (the Arabidopsis Genome Initiative; http://genome-www. stanford.edu/Arabidopsis/agi.html). To support the genome-sequencing effort, we fingerprinted more than 20,000 BACs (ref. 2) from two high-quality publicly available libraries, generating an estimated 17-fold redundant coverage of the genome, and used the fingerprints to nucleate assembly of the data by computer. Subsequent manual revision of the assemblies resulted in the incorporation of 19,661 fingerprinted BACs into 169 ordered sets of overlapping clones ('contigs'), each containing at least 3 clones. These contigs are ideal for parallel selection of BACs for large-scale sequencing and have supported the generation of more than 5.8 Mb of finished genome sequence submitted to GenBank; analysis of the sequence has confirmed the integrity of contigs constructed using this fingerprint data. Placement of contigs onto chromosomes can now be performed, and is being pursued by groups involved in both sequencing and positional cloning studies. To our knowledge, these data provide the first example of whole-genome random BAC fingerprint analysis of a eucaryote, and have provided a model essential to efforts aimed at generating similar databases of fingerprint contigs to support sequencing of other complex genomes, including that of human.

Arabidopsis↗
PubMed1999

A complete BAC-based physical map of the Arabidopsis thaliana genome.

Arabidopsis thaliana is a small flowering plant that serves as the major model system in plant molecular genetics. The efforts of many scientists have produced genetic maps that provide extensive coverage of the genome (http://genome-www. stanford.edu/Arabidopsis/maps.html). Recently, detailed YAC, BAC, P1 and cosmid-based physical maps (that is, representations of genomic regions as sets of overlapping clones of corresponding libraries) have been established that extend over wide genomic areas ranging from several hundreds of kilobases to entire chromosomes. These maps provide an entry to gain deeper insight into the A. thaliana genome structure. A. thaliana has been chosen as the subject of the first large-scale project intended to determine the full genome sequence of a plant. This sequencing project, together with the increasing interest in map-based gene cloning, has highlighted the requirement for a complete and accurate physical map of this plant species. To supply the scientific community with a high-quality resource, we present here a complete physical map of A. thaliana using essentially the IGF BAC library. The map consists of 27 contigs that cover the entire genome, except for the presumptive centromeric regions, nucleolar organization regions (NOR) and telomeric areas. This is the first reported map of a complex organism based entirely on BAC clones and it represents the most homogeneous and complete physical map established to date for any plant genome. Furthermore, the analysis performed here serves as a model for an efficient physical mapping procedure using BAC clones that can be applied to other complex genomes.

Arabidopsis↗
PubMed1998

Chromosomal imprinting in plants.

Chromosomal imprints in the broadest sense can arise in somatic as well as germline cells. They can be imposed through the modification of chromosomal proteins or by the modification of chromosomal DNA, and they typically effect the expression of nearby genes. Modification enzymes--such as histone deacetylases and cytosine methyltransferases, as well as chromatin components--are known to play this role in animals and many of these same enzymes and components have been found in plants. Transposable elements are subject to chromosomal imprinting and may play a fundamental role in this process in plant and other eukaryotic genomes.

Animals↗
PubMed1998

Old and new pathways of protein export in chloroplasts and bacteria.

Targeting of chloroplast proteins to the thylakoid membrane is analogous to bacterial secretion, and much of what we know has been learned from secretory mechanisms in Escherichia coli. However, chloroplasts also use a delta pH-dependent pathway to target thylakoid proteins, at least some of which are folded before transport. Previously, this pathway seemed to have no cognate in bacteria, but recent results have shown that the HCF106 gene in maize encodes a component of this pathway and has bacterial homologues. This delta pH-dependent pathway might be an ancient conserved mechanism for protein translocation that evolved before the endosymbiotic origin of plastids and mitochondria.

Amino Acid Sequence↗