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Andrew J Fleming

Publications and source records attributed to Andrew J Fleming.

13 recordsLinked to original sources
PubMed2006

Zimmermann's telome theory of megaphyll leaf evolution: a molecular and cellular critique.

Megaphyll leaf evolution was a critical event in Earth history that had major consequences for the biotic regulation of the global environment. Zimmermann's telome theory has been widely accepted for over seventy years as the leading explanation for this evolutionary innovation. According to the telome theory, megaphylls evolved from the three-dimensional lateral branches of early vascular land plants in a hypothetical series of three transformations; first, the formation of determinate lateral branches (overtopping); second, the development of 'flattened' branch systems (planation); and third, the fusion of planated branches with lateral outgrowths of photosynthetic mesophyll tissue to form the leaf blade (webbing). A critical review of the molecular and cellular evidence identifies plausible genetic, cellular and physiological mechanisms in extant higher plants for overtopping and planation but more limited evidence for the process of webbing (lateral outgrowth fusion). We highlight key outstanding questions concerning the telome theory that are likely to be resolved when gene identification and functional analysis techniques are applied to photosynthetic organisms that have different evolutionary histories.

Biological Evolution↗
PubMed2006

Plant signalling: the inexorable rise of auxin.

The flow of signalling molecules across a field of cells to generate a pattern that is then transduced into a differential response in those cells is a fundamental concept in developmental biology. Recent studies have identified a system that regulates the flux of the growth factor auxin through plant tissues via the subcellular asymmetric localization of specific transporters. The recurrent use of this auxin transport system in different developmental and physiological contexts reveals a fundamental mechanism underpinning organogenesis, stem cell positioning and the growth response of the plant to the environment. Here, I will discuss key advances in the identification of auxin transporters and their integration with auxin signal transduction pathways.

Arabidopsis Proteins↗
PubMed2006

Induction of differentiation in the shoot apical meristem by transient overexpression of a retinoblastoma-related protein.

The shoot apical meristem contains cells that undergo continual growth and division to generate the building blocks for the aerial portion of the plant. As cells leave the meristem, they undergo differentiation to form specific cell types. Most notably, heterotrophic cells of the meristem rapidly gain autotrophic capability by synthesis and assembly of components of the chloroplast. At the same time, cells undergo enlargement via vacuolation. Despite significant advances in the characterization of transcriptional networks involved in meristem maintenance and leaf determination, our understanding of the actual mechanism of meristem cell differentiation remains very limited. Using a microinduction technique, we show that local, transient overexpression of a retinoblastoma-related (RBR) protein in the shoot apical meristem is sufficient to trigger cells in the meristem to undergo the initial stages of differentiation. Taken together with recent data showing that RBR protein plays a key role in restricting stem cell differentiation in the root apical meristem, our data contribute to an emerging picture of RBR proteins as a central part of the mechanism controlling meristem cell differentiation.

Arabidopsis↗
PubMed2006

Leaf initiation: the integration of growth and cell division.

The shoot apical meristem of higher plants is characterized by a conserved pattern of cell division, the functional significance of which is unclear. Although a causal role for cell division frequency and orientation in morphogenesis has been suggested, supporting data are limited. An alternative interpretation laying stress on the control of growth vector and its integration with networks of transcription factors and hormonal signals is discussed in this review.

Cell Division↗
PubMed2005

The co-ordination of cell division, differentiation and morphogenesis in the shoot apical meristem: a perspective.

Whether morphogenesis is cell division-driven or organismal-based has been a long-running debate in plant biology. This article is a summary of a series of experiments aimed at distinguishing these alternate views by local manipulation of parameters of cell division frequency, orientation, and growth within the shoot apical meristem. These data, put in the context of other investigations in this area, support an organismal view of plant morphogenesis and support the idea that the cell wall plays a key role in the mechanism by which this is achieved. At the same time, the data indicate that the intimate but variable relationship between cell growth and division within the organism means that cell proliferation can indirectly influence this process, leading to a context-dependent influence on morphogenesis. Finally, cell growth and proliferation are intimately related with the process of differentiation as cells exit the meristem. In the final part of the article the molecular mechanism by which these basic cellular parameters are intertwined is discussed.

Cell Differentiation↗
PubMed2005

The integration of cell proliferation and growth in leaf morphogenesis.

A number of recent publications have assessed the outcome on leaf development of targeted manipulation of cell proliferation. The results of these investigations have awakened interest in the long-standing debate in plant biology on the precise role of cell division in morphogenesis. Does cell proliferation drive morphogenesis (cell theory) or is it subservient to a mechanism which acts at the whole organ level to regulate morphogenesis (organismal theory)? In this review, the central role of growth processes (distinct from cell proliferation) in morphogenesis is highlighted and the limitations in our understanding of the basic mechanisms of plant growth control are highlighted. Finally, an attempt is made to demonstrate how sequential local co-ordination of growth might provide an interpretation of some of the recent observations on cell proliferation and leaf morphogenesis.

Cell Proliferation↗
PubMed2005

Formation of primordia and phyllotaxy.

Leaves are made in an iterative pattern by the shoot apical meristem. The mechanism of this pattern formation has fascinated biologists, mathematicians and poets for centuries. Over the past year, fundamental insights into the molecular basis of this process have been gained. Patterns of auxin polar transport dictate when and where new leaf primordia are formed on the surface of the apical meristem. Subsequent events are still obscure but appear to involve both alteration of cell wall characteristics (to facilitate a new vector of growth) and a cascade of spatially co-ordinated transcription factor activity (to determine the fate of cells that are incorporated into new lateral organs). The co-ordinated signalling events involved in these processes are beginning to be elucidated.

Gene Expression Regulation, Developmental↗
PubMed2005

The control of leaf development.

The formation of a leaf is a basic aspect of plant development. This review provides an overview of our present understanding of the process from initiation to the final form of the leaf. Molecular genetic and cell biology approaches have yielded significant advances in this area, adding not only to our knowledge of leaf development but also to fundamental principles in plant biology. These principles will be highlighted, as well as areas where our understanding is still incomplete, in particular the problem of coordinating the multifaceted steps involved in the generation of the leaf structure.

Cell Differentiation↗
PubMed2002

The mechanism of leaf morphogenesis.

Whether cell division is a driving force in plant morphogenesis has long been debated. In this review, the evidence for the existence of cell division-dependent and cell division-independent mechanisms of plant morphogenesis is discussed. The potential mechanisms themselves are then analysed, as is our understanding of the regulation of these mechanisms and how they are integrated into development, with particular emphasis on data arising from the investigation of leaf morphogenesis. The analysis indicates the existence of both cell division-dependent and cell division-independent mechanisms in leaf morphogenesis and highlights the importance of future investigations to unravel the co-ordination of these mechanisms.

Cell Division↗
PubMed2002

The ABC transporter SpTUR2 confers resistance to the antifungal diterpene sclareol.

PDR5-like proteins represent one group of the ABC superfamily of transporters. Members of this group are present in plants and, due to the function of PDR5-related proteins in fungi in the excretion of xenobiotics (including antifungal agents), it has been proposed that they might play a similar role in plants in the response to and detoxification of herbicides and fungicides. However, until now no functional data has been presented showing an altered plant response to any herbicide or fungicide as a result of manipulating the expression of a PDR5-like gene in plants. In this paper, we show that the plant SpTUR2 PDR5-like ABC transporter is localised to the plasma membrane and that expression of this protein in Arabidopsis leads to the acquisition of resistance to the diterpenoid antifungal agent sclareol. These data both define a possible endogenous substrate for this transporter and highlight the potential of manipulating plant chemical resistance via modulating the expression of specific PDR5-like transporters.

ATP-Binding Cassette Transporters↗
PubMed2002

Manipulation of leaf shape by modulation of cell division.

The role of cell division as a causal element in plant morphogenesis is debatable, with accumulating evidence supporting the action of cell division-independent mechanisms. To directly test the morphogenic function of cell division, we have utilised a microinduction technique to locally and transiently manipulate the expression in transgenic plants of two genes encoding putative effectors of the cell cycle, a tobacco A-type cyclin and a yeast cdc25. The results show that local expression of these genes leads to modulation of cell division patterns. Moreover, whereas altered cell division in the apical meristem had no influence on organogenesis, local induction of cell proliferation on the flanks of young leaf primordia led to a dramatic change in lamina development and, thus, leaf shape. These data indicate that the role of cell division in plant morphogenesis is context dependent and identify cell division in the leaf primordium as a potential target for factors regulating leaf shape.

Cell Division↗