Biomedical subjects

Mary E Byrne

Publications and source records attributed to Mary E Byrne.

6 recordsLinked to original sources

PubMed2006

Specification of leaf polarity in Arabidopsis via the trans-acting siRNA pathway.

Plants leaves develop proximodistal, dorsoventral (adaxial-abaxial), and mediolateral patterns following initiation. The Myb domain gene PHANTASTICA (PHAN) is required for adaxial fate in many plants , but the Arabidopsis ortholog ASYMMETRIC LEAVES1 (AS1) has milder effects, suggesting that alternate or redundant pathways exist . We describe enhancers of as1 with more elongate and dissected leaves. As well as RDR6, an RNA-dependent RNA polymerase previously proposed to influence as1 through microRNA , these enhancers disrupt ARGONAUTE7 (AGO7)/ZIPPY, SUPPRESSOR OF GENE SILENCING3 (SGS3), and DICER-LIKE4 (DCL4), which instead regulate trans-acting small interfering RNA (ta-siRNA) . Microarray analysis revealed that the AUXIN RESPONSE FACTOR genes ETTIN (ETT)/ARF3 and ARF4 were upregulated in ago7, whereas FILAMENTOUS FLOWER (FIL) was upregulated only in as1 ago7 double mutants. RDR6 and SGS3 likewise repress these genes, which specify abaxial fate . We show that the trans-acting siRNA gene TAS3, which targets ETT and ARF4, is expressed in the adaxial domain, and ett as1 ago7 triple mutants resemble as1. Thus FIL is downregulated redundantly by AS1 and by TAS3, acting through ETT, revealing a role for ta-siRNA in leaf polarity. RDR6 and DCL4 are required for systemic silencing, perhaps implicating ta-siRNA as a mobile signal.

Arabidopsis↗

PubMed2006

Shoot meristem function and leaf polarity: the role of class III HD-ZIP genes.

The shoot apical meristem comprises an organized cluster of cells with a central region population of self-maintaining stem cells providing peripheral region cells that are recruited to form differentiated lateral organs. Leaves, the principal lateral organ of the shoot, develop as polar structures typically with distinct dorsoventrality. Interdependent interactions between the meristem and developing leaf provide essential cues that serve both to maintain the meristem and to pattern dorsoventrality in the initiating leaf. A key component of both processes are the class III HD-ZIP genes. Current findings are defining the developmental role of members of this family and are identifying multiple mechanisms controlling expression of these genes.

Arabidopsis Proteins↗

PubMed2005

Networks in leaf development.

Shoots are characterized by indeterminate growth resulting from divisions of undifferentiated cells in the central region of the shoot apical meristem. These cells give rise to peripheral derivatives from which lateral organ initials are recruited. During initial stages of cell recruitment, the three-dimensional form of lateral organs is specified. Lateral organs such as leaves develop and differentiate along proximodistal (base-to-tip), dorsoventral (top-to bottom) and mediolateral (middle-to-margin) planes. Current findings are refining our knowledge of the genes and genetic interactions that regulate these early processes and are providing a picture of how these pathways may contribute to variation in leaf form.

Gene Expression Regulation, Developmental↗

PubMed2003

Plant stem cells: divergent pathways and common themes in shoots and roots.

Stem cells in plant shoot and root meristems are maintained throughout the life of the plant and produce somatic daughter cells that make up the body of the plant. Plant stem cells can also be derived from somatic cells in vivo and in vitro. Recent findings are refining our knowledge of signaling pathways that define stem cell fate and specify either shoot or root stem cell function. New evidence also highlights a role for epigenetic mechanisms in controlling stem cell fate.

Cell Communication↗

PubMed2003

Phyllotactic pattern and stem cell fate are determined by the Arabidopsis homeobox gene BELLRINGER.

Lateral organs in plants arise from the meristem in a stereotypical pattern known as phyllotaxy. Spiral patterns result from initiation of successive organs at a fixed angle of divergence but variable patterns of physical contact. Such patterns ultimately give rise to individual leaves and flowers at positions related to each other by consecutive terms in the mathematical series first described by Leonardo Fibonacci. We demonstrate that a BELL1 related homeodomain protein in Arabidopsis, BELLRINGER, maintains the spiral phyllotactic pattern. In the absence of BELLRINGER, the regular pattern of organ initiation is disturbed and lateral organs are initiated more frequently. BELLRINGER is also required for maintenance of stem cell fate in the absence of the regulatory genes SHOOT MERISTEMLESS and ASYMMETRIC LEAVES1. We propose a model whereby BELLRINGER coordinates the maintenance of stem cells with differentiation of daughter cells in stem cell lineages.

Arabidopsis↗

PubMed2002

ASYMMETRIC LEAVES1 reveals knox gene redundancy in Arabidopsis.

The shoot apical meristem comprises undifferentiated stem cells and their derivatives, which include founder cells for lateral organs such as leaves. Meristem maintenance and lateral organ specification are regulated in part by negative interactions between the myb domain transcription factor ASYMMETRIC LEAVES1, which is expressed in lateral organ primordia, and homeobox transcription factors which are expressed in the shoot apical meristem (knox genes). The knox gene SHOOT MERISTEMLESS (STM) negatively regulates ASYMMETRIC LEAVES1 (AS1) which, in turn, negatively regulates other knox genes including KNAT1 and KNAT2, and positively regulates the novel gene LATERAL ORGAN BOUNDARIES (LOB). Genetic interactions with a second gene, ASYMMETRIC LEAVES2 (AS2), indicate it acts at the same position in this hierarchy as AS1. We have used a second-site suppressor screen to isolate mutations in KNAT1 and we show that KNAT1 is partially redundant with STM in regulating stem cell function. Mutations in KNAT2 show no such interaction. We discuss the regulation and evolution of redundancy among knox genes.

Amino Acid Sequence↗