Genetic approach towards the identification of auxin - cytokinin crosstalk components involved in root development

Department of Plant Systems Biology, VIB, Technologiepark 927, 9052 Ghent, Belgium.
Philosophical Transactions of The Royal Society B Biological Sciences (Impact Factor: 7.06). 06/2012; 367(1595):1469-78. DOI: 10.1098/rstb.2011.0233
Source: PubMed


Phytohormones are important plant growth regulators that control many developmental processes, such as cell division, cell differentiation, organogenesis and morphogenesis. They regulate a multitude of apparently unrelated physiological processes, often with overlapping roles, and they mutually modulate their effects. These features imply important synergistic and antagonistic interactions between the various plant hormones. Auxin and cytokinin are central hormones involved in the regulation of plant growth and development, including processes determining root architecture, such as root pole establishment during early embryogenesis, root meristem maintenance and lateral root organogenesis. Thus, to control root development both pathways put special demands on the mechanisms that balance their activities and mediate their interactions. Here, we summarize recent knowledge on the role of auxin and cytokinin in the regulation of root architecture with special focus on lateral root organogenesis, discuss the latest findings on the molecular mechanisms of their interactions, and present forward genetic screen as a tool to identify novel molecular components of the auxin and cytokinin crosstalk.

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Available from: Peter Marhavy, Mar 19, 2015
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    • "Cytokinins are also well known to influence the root architecture (reviewed in Vanstraelen and Benková, 2012). Cytokinin signaling negatively affects LR development by impinging on PIN-dependent auxin transport (Laplaze et al., 2007; Bishopp et al., 2011; Marhavý et al., 2011, 2014; Bielach et al., 2012; Chang et al., 2013; Moreira et al., 2013). Interaction of SLs with cytokinins during LR development has been poorly studied, but max2-1 mutants have been reported to have a reduced sensitivity to the synthetic cytokinin 6-benzylaminopurine (BAP) (Koren et al., 2013). "
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    ABSTRACT: Strigolactones are important rhizosphere signals that act as phytohormones and have multiple functions, including modulation of lateral root (LR) development. Here, we show that treatment with the strigolactone analog GR24 did not affect LR initiation, but negatively influenced LR priming and emergence, the latter especially near the root–shoot junction. The cytokinin module ARABIDOPSIS HISTIDINE KINASE3 (AHK3)/ARABIDOPSIS RESPONSE REGULATOR1 (ARR1)/ARR12 was found to interact with the GR24-dependent reduction in LR development, because mutants in this pathway rendered LR development insensitive to GR24. Additionally, pharmacological analyses, mutant analyses, and gene expression analyses indicated that the affected polar auxin transport stream in mutants of the AHK3/ARR1/ARR12 module could be the underlying cause. Altogether, the data reveal that the GR24 effect on LR development depends on the hormonal landscape that results from the intimate connection with auxins and cytokinins, two main players in LR development.
    Full-text · Article · Oct 2015 · Journal of Experimental Botany
    • "i.e. auxin induces cell division in the meristems, while cytokinin stimulates the differentiation of these cells (reviewed inBielach et al., 2012;Bishopp, Benkov a, & Helariutta, 2011;Moubayidin, Di Mambro, & Sabatini, 2009;Saini, Sharma, Kaur, & Pati, 2013). Hormone signalling function in the plant–nematode interaction is not restricted to the interference with developmental pathways to establish the feeding site as they also play a key role in plant defences (review in Chapter 6). "
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    ABSTRACT: Sedentary plant endoparasitic (root-knot and cyst) nematodes induce the formation of their feeding sites by directing the transdifferentiation of normal plant root cells into nematode feeding cells, namely giant cells (GCs) and syncytia. In the past years, transcriptomic analyses combined with molecular cell biology have revealed dramatic and specific changes in gene expression in syncytia and GCs. Among the genes whose expression is modified to establish feeding sites are those involved in hormone-regulated developmental pathways in the roots, particularly those related to auxins and cytokinins. The high concentrations of auxins and cytokinins in galls and syncytia have been described in detail by the use of reporter genes driven by specific promoters as ‘sensors’ of both phytohormones, such as DR5, ARR5 or TCS. Moreover, several molecular evidences link the formation of nematode feeding sites (NFSs) to developmental processes such as maintenance of the root apical meristem, lateral root initiation or vascular tissue development, in which the two hormones are involved. The mechanisms that nematodes use to interfere with plant developmental pathways are unclear, but some seem to involve nematode secreted molecules, such as the CLE-like and the CEP peptides. Only in a few cases, plant hormone transduction and developmental circuits hijacked by nematodes to induce and maintain feeding sites have been studied in detail. Analysis combining hormone genetic sensors, mutants and comparative transcriptomics lead to the identification of relevant plant regulators that are exploited for NFS differentiation. We present the current knowledge connecting the hormonal-controlled developmental processes of the root with the development of the NFS, which seem to be different for GCs and syncytia. For instance, LBD16 and WRKY23, two key transcription factors in the signal transduction leading to lateral root formation mediated by auxins, play distinctive roles during gall/GC and syncytia formation, respectively. However, the expression of either gene in the feeding site is not strictly plant auxin-dependent, indicating that their regulation by nematodes differs in some aspects from the endogenous pathways operating in normal root development. We also highlight the evidences linking gall and GC ontogeny to the pericycle and discuss the transfer cell-like identity of feeding cells.
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    • "The root-apex TZ is a critical site for the perception and response to both endogenous phytohormones and environmental cues (Baluška et al., 2010), particularly to auxin, the key regulator of root development (Benková and Hejátko, 2009; Overvoorde et al., 2010; Bielach et al., 2012; Jansen et al., 2012; Lavenus et al., 2013). In conjunction with auxin, ethylene is also involved in the regulation of root growth (R uzicka et al., 2007; Swarup et al., 2007). "
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    ABSTRACT: The transition zone (TZ) of the root apex is the perception site of Al toxicity. Here, we show that exposure of Arabidopsis thaliana roots to Al induces a localized enhancement of auxin signaling in the root-apex TZ that is dependent on TAA1, which encodes a Trp aminotransferase and regulates auxin biosynthesis. TAA1 is specifically upregulated in the root-apex TZ in response to Al treatment, thus mediating local auxin biosynthesis and inhibition of root growth. The TAA1-regulated local auxin biosynthesis in the root-apex TZ in response to Al stress is dependent on ethylene, as revealed by manipulating ethylene homeostasis via the precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid, the inhibitor of ethylene biosynthesis aminoethoxyvinylglycine, or mutant analysis. In response to Al stress, ethylene signaling locally upregulates TAA1 expression and thus auxin responses in the TZ and results in auxin-regulated root growth inhibition through a number of auxin response factors (ARFs). In particular, ARF10 and ARF16 are important in the regulation of cell wall modification-related genes. Our study suggests a mechanism underlying how environmental cues affect root growth plasticity through influencing local auxin biosynthesis and signaling.
    Full-text · Article · Jul 2014 · The Plant Cell
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