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Jennifer C Fletcher

Publications and source records attributed to Jennifer C Fletcher.

18 recordsLinked to original sources
PubMed2006

The E3 ubiquitin ligase BIG BROTHER controls arabidopsis organ size in a dosage-dependent manner.

Organ growth up to a species-specific size is tightly regulated in plants and animals. Final organ size is remarkably constant within a given species, suggesting that a species-specific size checkpoint terminates organ growth in a coordinated and timely manner. Phytohormones influence plant organ size, but their precise functions in size control are unclear because of their pleiotropic and complex developmental roles. The Arabidopsis transcription factors AINTEGUMENTA and JAGGED promote organ growth by maintaining cellular proliferation potential. Loss of the Antirrhinum transcription factor CINCINNATA causes leaf overgrowth, yet also leads to a highly abnormal leaf shape. Thus, no dedicated factor that limits the final size of plant organs has been isolated. Here, we identify the novel RING-finger protein BIG BROTHER (BB) as a repressor of plant organ growth. Small changes in BB expression levels substantially alter organ size, indicating a central regulatory role for BB in growth control. Recombinant BB protein has E3 ubiquitin-ligase activity that is essential for its in vivo function, suggesting that BB acts by marking cellular proteins for degradation. Our data indicate that plants limit the duration of organ growth and ultimately organ size by actively degrading critical growth stimulators.

Amino Acid Sequence↗
PubMed2006

RABBIT EARS is a second-whorl repressor of AGAMOUS that maintains spatial boundaries in Arabidopsis flowers.

The RABBIT EARS (RBE) gene has been identified as a regulator of petal development in Arabidopsis thaliana. We find that second-whorl petals in rbe mutants can be replaced with staminoid organs, stamens or filaments and that some rbe flowers have increased numbers of sepals and exhibit fusion of sepals. We show that these rbe defects are due to AGAMOUS (AG) misexpression in the second whorl. Consistent with its role in maintaining the spatial boundary of AG expression, rbe enhanced the second-whorl defects present in ap2-1, lug-1 and clf-2 mutants. In the development of second-whorl organs, RBE acts in the same pathway and downstream of UNUSUAL FLORAL ORGANS (UFO). Enhanced first-whorl organ fusion in ap2-2 rbe-3, ant-4 rbe-3 and cuc2-1 rbe-3 double mutants supports an additional role for RBE in organ separation. RBE thus acts to maintain two different types of spatial boundaries in young flowers: boundaries between organ primordia within a whorl and boundaries of homeotic gene expression between whorls.

AGAMOUS Protein, Arabidopsis↗
PubMed2005

Stem cell regulation in the Arabidopsis shoot apical meristem.

The aerial structure of higher plants is generated dynamically throughout the life cycle through the activity of stem cells that are located at the growing shoot tip, the apical meristem. The stem cells continuously divide to renew themselves and provide cells for leaf, stem and flower formation. Stem cell maintenance is governed by intercellular communication between the apical stem cells and the underlying organizing centre. Recent advances have been made in understanding the mechanisms that induce shoot stem cell identity, and that control the position and size of the organizing centre. Elements such as chromatin remodeling factors, transcription factors and microRNAs are newly implicated in these regulatory processes. These advances provide a framework for our understanding of how signals are integrated to specify and position the stem cell niche in the shoot apical meristem.

Arabidopsis↗
PubMed2005

Regulation of Arabidopsis shoot apical meristem and lateral organ formation by microRNA miR166g and its AtHD-ZIP target genes.

Plant development is characterized by precise control of gene regulation, leading to the correct spatial and temporal tissue patterning. We have characterized the Arabidopsis jabba-1D (jba-1D) mutant, which displays multiple enlarged shoot meristems, radialized leaves, reduced gynoecia and vascular defects. The jba-1D meristem phenotypes require WUSCHEL (WUS) activity, and correlate with a dramatic increase in WUS expression levels. We demonstrate that the jba-1D phenotypes are caused by over-expression of miR166g, and require the activity of the RNase III helicase DCL1. miR166g over-expression in jba-1D plants affects the transcripts of several class III homeodomain-leucine zipper (AtHD-ZIP) family target genes. The expression of PHABULOSA (PHB), PHAVOLUTA (PHV) and CORONA (CNA) is significantly reduced in a jba-1D background, while REVOLUTA (REV) expression is elevated and ATHB8 is unchanged. In addition, we show that miR166 has a dynamic expression pattern in wild-type and jba-1D embryos. Our analysis demonstrates an indirect role for miRNAs in controlling meristem formation via regulation of WUS expression, and reveals complex regulation of the class III AtHD-ZIP gene family.

Amino Acid Sequence↗
PubMed2005

A database analysis method identifies an endogenous trans-acting short-interfering RNA that targets the Arabidopsis ARF2, ARF3, and ARF4 genes.

Two classes of small RNAs, microRNAs and short-interfering RNA (siRNAs), have been extensively studied in plants and animals. In Arabidopsis, the capacity to uncover previously uncharacterized small RNAs by means of conventional strategies seems to be reaching its limits. To discover new plant small RNAs, we developed a protocol to mine an Arabidopsis nonannotated, noncoding EST database. Using this approach, we identified an endogenous small RNA, trans-acting short-interfering RNA-auxin response factor (tasiR-ARF), that shares a 21- and 22-nt region of sequence similarity with members of the ARF gene family. tasiR-ARF has characteristics of both short-interfering RNA and microRNA, recently defined as tasiRNA. Accumulation of trans-acting siRNA depends on DICER-LIKE1 and RNA-DEPENDENT RNA POLYMERASE6 but not RNA-DEPENDENT RNA POLYMERASE2. We demonstrate that tasiR-ARF targets three ARF genes, ARF2, ARF3/ETT, and ARF4, and that both the tasiR-ARF precursor and its target genes are evolutionarily conserved. The identification of tasiRNA-ARF as a low-abundance, previously uncharacterized small RNA species proves our method to be a useful tool to uncover additional small regulatory RNAs.

Arabidopsis↗
PubMed2005

ULTRAPETALA1 encodes a SAND domain putative transcriptional regulator that controls shoot and floral meristem activity in Arabidopsis.

The higher-plant shoot apical meristem is a dynamic structure continuously producing cells that become incorporated into new leaves, stems and flowers. The maintenance of a constant flow of cells through the meristem depends on coordination of two antagonistic processes: self-renewal of the stem cell population and initiation of the lateral organs. This coordination is stringently controlled by gene networks that contain both positive and negative components. We have previously defined the ULTRAPETALA1 (ULT1) gene as a key negative regulator of cell accumulation in Arabidopsis shoot and floral meristems, because mutations in ULT1 cause the enlargement of inflorescence and floral meristems, the production of supernumerary flowers and floral organs, and a delay in floral meristem termination. Here, we show that ULT1 negatively regulates the size of the WUSCHEL (WUS)-expressing organizing center in inflorescence meristems. We have cloned the ULT1 gene and find that it encodes a small protein containing a B-box-like motif and a SAND domain, a DNA-binding motif previously reported only in animal transcription factors. ULT1 and its Arabidopsis paralog ULT2 define a novel small gene family in plants. ULT1 and ULT2 are expressed coordinately in embryonic shoot apical meristems, in inflorescence and floral meristems, and in developing stamens, carpels and ovules. Additionally, ULT1 is expressed in vegetative meristems and leaf primordia. ULT2 protein can compensate for mutant ULT1 protein when overexpressed in an ult1 background, indicating that the two genes may regulate a common set of targets during plant development. Downregulation of both ULT genes can lead to shoot apical meristem arrest shortly after germination, revealing a requirement for ULT activity in early development.

Alleles↗
PubMed2005

Molecular mechanisms of flower development: an armchair guide.

An afternoon stroll through an English garden reveals the breathtaking beauty and enormous diversity of flowering plants. The extreme variation of flower morphologies, combined with the relative simplicity of floral structures and the wealth of floral mutants available, has made the flower an excellent model for studying developmental cell-fate specification, morphogenesis and tissue patterning. Recent molecular genetic studies have begun to reveal the transcriptional regulatory cascades that control early patterning events during flower formation, the dynamics of the gene-regulatory interactions, and the complex combinatorial mechanisms that create a distinct final floral architecture and form.

Cell Differentiation↗
PubMed2004

HANABA TARANU is a GATA transcription factor that regulates shoot apical meristem and flower development in Arabidopsis.

We have isolated a new mutant, hanaba taranu (han), which affects both flower and shoot apical meristem (SAM) development in Arabidopsis thaliana. Mutants have fused sepals and reduced organ numbers in all four whorls, especially in the 2nd (petal) and 3rd (stamen) whorls. han meristems can become flatter or smaller than in the wild type. HAN encodes a GATA-3-like transcription factor with a single zinc finger domain. HAN is transcribed at the boundaries between the meristem and its newly initiated organ primordia and at the boundaries between different floral whorls. It is also expressed in vascular tissues, developing ovules and stamens, and in the embryo. han interacts strongly with clavata (clv) mutations (clv1, clv2, and clv3), resulting in highly fasciated SAMs, and we find that WUS expression is altered in han mutants from early embryogenesis. In addition, HAN is ectopically expressed both in clv1 and clv3 mutants. We propose that HAN is normally required for establishing organ boundaries in shoots and flowers and for controlling the number and position of WUS-expressing cells. Ectopic HAN expression causes growth retardation, aberrant cell division patterns, and loss of meristem activity, suggesting that HAN is involved in controlling cell proliferation and differentiation.

Amino Acid Sequence↗
PubMed2004

BLADE-ON-PETIOLE1 encodes a BTB/POZ domain protein required for leaf morphogenesis in Arabidopsis thaliana.

The BLADE-ON-PETIOLE1 (BOP1) gene of Arabidopsis thaliana is required for proper leaf morphogenesis. BOP1 regulates leaf differentiation in a proximal-distal manner, and represses the expression of three class I knotted-like homeobox (knox) genes during leaf formation. Utilizing a map-based approach, we identified the molecular nature of the BOP1 gene, which encodes a BTB/POZ domain protein with ankyrin repeats. BOP1 is a member of a small gene family in Arabidopsis that includes the disease resistance regulatory protein NPR1. Insertions in and around BOP1 cause distinct lesions in leaf morphogenesis, revealing complex regulation of the locus. BOP1 transcripts are initially detectable in embryos, where they specifically localize to the base of the developing cotyledons near the SAM. During vegetative development, BOP1 is expressed in young leaf primordia and at the base of the rosette leaves on the adaxial side. During reproductive development, BOP1 transcripts are detected in young floral buds, and at the base of the sepals and petals. Our results indicate that BOP1 encodes a putative regulatory protein that modulates meristematic activity at discrete locations in developing lateral organs. This is the first report on a plant protein that plays a key role in morphogenesis with the distinctive combinatorial architecture of the BTB/POZ and ankyrin repeat domains.

Amino Acid Sequence↗
PubMed2004

The ULTRAPETALA1 gene functions early in Arabidopsis development to restrict shoot apical meristem activity and acts through WUSCHEL to regulate floral meristem determinacy.

Shoot and floral meristem activity in higher plants is controlled by complex signaling networks consisting of positive and negative regulators. The Arabidopsis ULTRAPETALA1 (ULT1) gene has been shown to act as a negative regulator of meristem cell accumulation in inflorescence and floral meristems, as loss-of-function ult1 mutations cause inflorescence meristem enlargement, the production of extra flowers and floral organs, and a decrease in floral meristem determinacy. To investigate whether ULT1 functions in known meristem regulatory pathways, we generated double mutants between ult1 alleles and null alleles of the meristem-promoting genes SHOOTMERISTEMLESS (STM) and WUSCHEL (WUS). We found that, although the ult1 alleles have no detectable embryonic or vegetative phenotypes, ult1 mutations restored extensive organ-forming capability to stm null mutants after germination and increased leaf and floral organ production in stm partial loss-of-function mutants. Mutations in ULT1 also partially suppressed the wus shoot and floral meristem phenotypes. However, wus was epistatic to ult1 in the center of the flower, and WUS transcriptional repression was delayed in ult1 floral meristems. Our results show that during the majority of the Arabidopsis life cycle, ULT1 acts oppositely to STM and WUS in maintaining meristem activity and functions in a separate genetic pathway. However, ULT1 negatively regulates WUS to establish floral meristem determinacy, acting through the WUS-AG temporal feedback loop.

Arabidopsis↗
PubMed2003

Maintenance of stem cell populations in plants.

Flowering plants have the unique ability to produce new organs continuously, for hundreds of years in some species, from stem cell populations maintained at their actively growing tips. The shoot tip is called the shoot apical meristem, and it acts as a self-renewing source of undifferentiated, pluripotent stem cells whose descendents become incorporated into organ and tissue primordia and acquire different fates. Stem cell maintenance is an active process, requiring constant communication between different regions of the shoot apical meristem to coordinate loss of stem cells from the meristem through differentiation with their replacement through cell division. Stem cell research in model plant systems is facilitated by the fact that mutants with altered meristem cell identity or accumulation are viable, allowing dissection of stem cell behavior by using genetic, molecular, and biochemical methods. Such studies have determined that in the model plant Arabidopsis thaliana stem cell maintenance information flows via a signal transduction pathway that is established during embryogenesis and maintained throughout the life cycle. Signaling through this pathway results in the generation of a spatial feedback loop, involving both positive and negative interactions, that maintains stem cell homeostasis. Stem cell activity during reproductive development is terminated by a temporal feedback loop involving both stem cell maintenance genes and a phase-specific flower patterning gene. Our current investigations provide additional insights into the molecular mechanisms that regulate stem cell activity in higher plants.

Arabidopsis↗
PubMed2003

Shoot apical meristem maintenance: the art of a dynamic balance.

The aerial structure of higher plants derives from cells at the tip of the stem, in the shoot apical meristem (SAM). Throughout the life of a plant, the SAM produces stem tissues and lateral organs, and also regenerates itself. For correct growth, the plant must maintain a constant flow of cells through the meristem, where the input of dividing pluripotent stem cells offsets the output of differentiating cells. This flow depends on extracellular signaling within the SAM, governed by a spatial regulatory feedback loop that maintains a reservoir of stem cells, and on factors that prevent meristem cells from differentiating prematurely. The terminating floral meristem incorporates the spatial regulation scheme into a temporal regulation pathway involving flower patterning factors.

Arabidopsis↗
PubMed2003

The Arabidopsis CLV3-like (CLE) genes are expressed in diverse tissues and encode secreted proteins.

Members of the receptor-like kinase gene family play crucial regulatory roles in many aspects of plant development, but the ligands to which they bind are largely unknown. In Arabidopsis, the receptor kinase CLAVATA1 (CLV1) binds to the small secreted polypeptide CLV3, and three proteins act as key elements of a signal transduction pathway that regulates shoot apical meristem maintenance. To better understand the signal transduction mechanisms involving small polypeptides, we are studying 25 Arabidopsis CLV3/ESR (CLE) proteins that share a conserved C-terminal domain with CLV3 and three maize ESR proteins. Members of the CLE gene family were identified in database searches and only a few are known to be expressed. We have identified an additional member of the CLE gene family in Arabidopsis, which is more similar in gene structure to CLV3 than the other CLE genes. Phylogenetic analysis reveals that few of the putative CLE gene products are closely related, suggesting there may be little functional overlap between them. We show that 24 of the 25 Arabidopsis CLE genes are transcribed in one or more tissues during development, indicating that they do encode functional products. Many are widely expressed, but others are restricted to one or a few tissue types. We have also determined the sub-cellular localization of several CLE proteins, and find that they are exported to the plasma membrane or extracellular space. Our results suggest that the Arabidopsis CLE proteins, like CLV3, may function as secreted signaling molecules that act in diverse pathways during growth and development.

Amino Acid Sequence↗
PubMed2002

Coordination of cell proliferation and cell fate decisions in the angiosperm shoot apical meristem.

A unique feature of flowering plants is their ability to produce organs continuously, for hundreds of years in some species, from actively growing tips called apical meristems. All plants possess at least one form of apical meristem, whose cells are functionally analogous to animal stem cells because they can generate specialized organs and tissues. The shoot apical meristem of angiosperm plants acts as a continuous source of pluripotent stem cells, whose descendents become incorporated into organ primordia and acquire different fates. Recent studies are unveiling some of the molecular pathways that specify stem cell fate in the center of the shoot apical meristem, that confer organ founder cell fate on the periphery, and that connect meristem patterning elements with events at the cellular level. The results are providing important insights into the mechanisms through which shoot apical meristems integrate cell fate decisions with cellular proliferation and global regulation of growth and development.

Animals↗
PubMed2002

Plant development makes strides in Vermont.

Plants are an excellent system for studying developmental biology. Depending on the species, they can be easily transformed and mutagenized, undergo grafts, tolerate changes in chromosome number, and provide fertile offspring after wide species crosses. Most importantly, they are perpetually embryonic, and thus development unfolds throughout the life of a plant. At a recent FASEB meeting, scientists shared their discoveries about plant development, covering topics that ranged from the evolution of form to cellular differentiation. The meeting demonstrated that the genetic and cellular basis of plant development is currently an exciting and growing field of research.

Cell Differentiation↗
PubMed2002

CLV3 is localized to the extracellular space, where it activates the Arabidopsis CLAVATA stem cell signaling pathway.

Plant growth and development depends on the activity of a continuously replenished pool of stem cells within the shoot apical meristem to supply cells for organogenesis. In Arabidopsis, the stem cell-specific protein CLAVATA3 (CLV3) acts cell nonautonomously to restrict the size of the stem cell population, but the hypothesis that CLV3 acts as an extracellular signaling molecule has not been tested. We used genetic and immunological assays to show that CLV3 localizes to the apoplast and that export to the extracellular space is required for its function in activating the CLV1/CLV2 receptor complex. Apoplastic localization allows CLV3 to signal from the stem cell population to the organizing center in the underlying cells.

Arabidopsis↗
PubMed2002

Shoot and floral meristem maintenance in arabidopsis.

The shoot apical meristem (SAM) of higher plants functions as a site of continuous organogenesis within which a small pool of pluripotent stem cells replenishes the cells incorporated into lateral organs. This article summarizes recent results demonstrating that the fate of stem cells in Arabidopsis shoot and floral meristems is controlled by overlapping spatial and temporal signaling systems. Stem cell maintenance is an active process requiring constant communication between neighboring groups of SAM cells. Information flows via a ligand-receptor signal transduction pathway, resulting in the formation of a spatial feedback loop that stabilizes the size of the stem cell population. Termination of stem cell activity during flower development is achieved by a temporal feedback loop involving both stem cell maintenance genes and flower patterning genes. These investigations are providing exciting insights into the components and activities of the stem cell regulatory pathway and into the interaction of this pathway with molecular mechanisms that control floral patterning.

Arabidopsis↗