PIN1-Independent Leaf Initiation in Arabidopsis

Institute of Plant Sciences, University of Bern, CH-3013 Bern, Switzerland.
Plant physiology (Impact Factor: 6.84). 06/2012; 159(4):1501-10. DOI: 10.1104/pp.112.200402
Source: PubMed


Phyllotaxis, the regular arrangement of leaves and flowers around the stem, is a key feature of plant architecture. Current models propose that the spatiotemporal regulation of organ initiation is controlled by a positive feedback loop between the plant hormone auxin and its efflux carrier PIN-FORMED1 (PIN1). Consequently, pin1 mutants give rise to naked inflorescence stalks with few or no flowers, indicating that PIN1 plays a crucial role in organ initiation. However, pin1 mutants do produce leaves. In order to understand the regulatory mechanisms controlling leaf initiation in Arabidopsis (Arabidopsis thaliana) rosettes, we have characterized the vegetative pin1 phenotype in detail. We show that although the timing of leaf initiation in vegetative pin1 mutants is variable and divergence angles clearly deviate from the canonical 137° value, leaves are not positioned at random during early developmental stages. Our data further indicate that other PIN proteins are unlikely to explain the persistence of leaf initiation and positioning during pin1 vegetative development. Thus, phyllotaxis appears to be more complex than suggested by current mechanistic models.

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Available from: Daniel Kierzkowski, Oct 01, 2015
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    • "[2] Auxin is crucial for the regulation of zygotic embryo development,[3] [4] root development,[2] [5] [6] including initiation and emergence of lateral roots [7À9] and the development of leaves and flowers.[10] [11] It is involved in the response of plants to light and gravity, [5] [12] general shoot and root architecture,[13] [14] organ patterning and vascular development [15À17] and apical dominancy regulation.[18] Auxin is vital for the regulation of cell division, initiation and radial position of plant lateral organs [19] and is likely to be an important regulator of nodulation.[20] "
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    ABSTRACT: The phytohormone auxin is transported by two distinct pathways in plants. Indole-3-acetic acid is mainly transported throughout the plant by an unregulated bulk flow in the mature phloem. The major auxin distribution is regulated via direct transport from cell to cell, known as polar auxin transport (PAT). PAT is maintained by the coordinated action of efflux (PIN) and auxin influx (AUX/LAX) carrier proteins. In this study, we examine, compare and localize the expression of a gene encoding an auxin influx carrier (MtLAX3) from Medicago truncatula in the model plants M. truncatula, Lotus japonicus and Arabidopsis thaliana. Transgenic plants with overexpression and down-regulation of MtLAX3, as well as with expressed promMtLAX3 transcriptional reporters, were constructed for the three model species, using Agrobacterium-mediated transformation. Histochemical and transcriptional analyses revealed the expression of MtLAX3 during various stages of somatic embryogenesis and plant development, as well as during formation of symbiotic nodules. The alteration of the MtLAX3 expression, as well as its overexpression in the analysed model species, results in various abnormal phenotypes and disturbance of leaf and root development. The reported results show that MtLAX3 plays an important role in proper plant growth and development, modelling of the root system and the number of formed nodules and seeds.
    Biotechnology & Biotechnological Equipment 04/2015; 29(4):1-12. DOI:10.1080/13102818.2015.1031698 · 0.30 Impact Factor
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    • "The analysis of the er erl1 erl2 mutant advances our understanding of how auxin transport contributes to leaf initiation and vasculature development. First, in spite of severely disrupted auxin transport, the er erl1 erl2 mutant is able to produce leaf primordia (albeit more slowly), supporting the idea that there should be a PIN1-independent mechanism of leaf initiation (Guenot et al., 2012). Second, auxin transport into the inner layers of the meristem is believed to be a trigger for preprocambial cell selection (for review, see Scarpella and Helariutta, 2010). "
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    ABSTRACT: Leaves are produced postembryonically at the flanks of the shoot apical meristem. Their initiation is induced by a positive feedback loop between auxin and its transporter PIN1. The expression and polarity of PIN1 in the shoot apical meristem is thought to be regulated primarily by auxin concentration and flow. The formation of an auxin maximum in the L1 layer of the meristem is the first sign of leaf initiation and is promptly followed by auxin flow into the inner tissues, formation of the midvein, and appearance of the primordium bulge. The ERECTA family genes (ERfs) encode leucine-rich repeat receptor-like kinases and in Arabidopsis this gene family consists of ERECTA (ER), ERECTA-LIKE 1 (ERL1) and ERL2. Here we show that ERfs regulate auxin transport during leaf initiation. The shoot apical meristem of the er erl1 erl2 triple mutant produces leaf primordia at a significantly reduced rate and with altered phyllotaxy. This phenotype is likely to be due to deficiencies in auxin transport in the shoot apex, as judged by altered expression of PIN1, the auxin reporter DR5rev::GFP, and the auxin inducible genes MP, IAA1, and IAA19. In er erl1 erl2 auxin presumably accumulates in the L1 layer of the meristem, unable to flow into the vasculature of a hypocotyl. Our data demonstrate that ERfs are essential for PIN1 expression in the forming midvein of future leaf primordia and in the vasculature of emerging leaves.
    Plant physiology 07/2013; 162(4). DOI:10.1104/pp.113.218198 · 6.84 Impact Factor
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    • "Therefore, auxin synthesis is sufficient to induce leaf morphogenesis in the pin1 mutant despite the abnormal phyllotactic pattern. Some assumptions have been made to explain the residual phyllotactic pattern showed by pin1 plants, which include the involvement of other auxin transporters, auxin synthesis and auxin-independent mechanisms (Guenot et al. 2012). Modifications in the mechanical properties of cells are necessary to control morphogenesis at shoot tips. "
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    ABSTRACT: Morphological diversity exhibited by higher plants is essentially related to the tremendous variation of leaf shape. With few exceptions, leaf primordia are initiated postembryonically at the flanks of a group of undifferentiated and proliferative cells within the shoot apical meristem (SAM) in characteristic position for the species and in a regular phyllotactic sequence. Auxin is critical for this process, because genes involved in auxin biosynthesis, transport, and signaling are required for leaf initiation. Down-regulation of transcription factors (TFs) and cytokinins are also involved in the light-dependent leaf initiation pathway. Furthermore, mechanical stresses in SAM determine the direction of cell division and profoundly influence leaf initiation suggesting a link between physical forces, gene regulatory networks and biochemical gradients. After the leaf is initiated, its further growth depends on cell division and cell expansion. Temporal and spatial regulation of these processes determines the size and the shape of the leaf, as well as the internal structure. A complex array of intrinsic signals, including phytohormones and TFs control the appropriate cell proliferation and differentiation to elaborate the final shape and complexity of the leaf. Here, we highlight the main determinants involved in leaf initiation, epidermal patterning, and elaboration of lamina shape to generate small marginal serrations, more deep lobes or a dissected compound leaf. We also outline recent advances in our knowledge of regulatory networks involved with the unusual pattern of leaf development in epiphyllous plants as well as leaf morphology aberrations, such as galls after pathogenic attacks of pests.
    Plant Cell Reports 04/2013; 32(6). DOI:10.1007/s00299-013-1426-1 · 3.07 Impact Factor
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