Park, J. E. et al. GH3-mediated auxin homeostasis links growth regulation with stress adaptation response in Arabidopsis. J. Biol. Chem. 282, 10036-10046

Department of Agronomy and Horticulture, University of Nebraska at Lincoln, Lincoln, Nebraska, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2007; 282(13):10036-46. DOI: 10.1074/jbc.M610524200
Source: PubMed

ABSTRACT Plants constantly monitor environmental fluctuations to optimize their growth and metabolism. One example is adaptive growth occurring in response to biotic and abiotic stresses. Here, we demonstrate that GH3-mediated auxin homeostasis is an essential constituent of the complex network of auxin actions that regulates stress adaptation responses in Arabidopsis. Endogenous auxin pool is regulated, at least in part, through negative feedback by a group of auxin-inducible GH3 genes encoding auxin-conjugating enzymes. An Arabidopsis mutant, wes1-D, in which a GH3 gene WES1 is activated by nearby insertion of the (35)S enhancer, exhibited auxin-deficient traits, including reduced growth and altered leaf shape. Interestingly, WES1 is also induced by various stress conditions as well as by salicylic acid and abscisic acid. Accordingly, wes1-D was resistant to both biotic and abiotic stresses, and stress-responsive genes, such as pathogenesis-related genes and CBF genes, were upregulated in this mutant. In contrast, a T-DNA insertional mutant showed reduced stress resistance. We therefore propose that GH3-mediated growth suppression directs reallocation of metabolic resources to resistance establishment and represents the fitness costs of induced resistance.

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    • "Morphological adaptations, such as the development of a waxy cuticle, vasculature, stomata, more complex root systems, and a diverse set of molecular mechanisms, allow plants to live in sometimes extreme conditions. Numerous studies have elucidated the adaptations of plants to severe drought conditions (McDowell et al., 2008; Akhtar et al., 2012; Golldack et al., 2014), often by withholding water until wilting or by cutting leaves and letting them dry to impose severe water deficits (Iuchi et al., 2001; Llorente et al., 2002; Taji et al., 2002; Cheong et al., 2003, 2007; Tran et al., 2004; Umezawa et al., 2004, 2006; Cominelli et al., 2005; Chen et al., 2006; Nelson et al., 2007; Park et al., 2007; Zhu et al., 2007; Zhang et al., 2008). However, the sudden infliction of such severe drought is unlikely to reflect what naturally happens in the field. "
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    ABSTRACT: Although the response of plants exposed to severe drought stress has been studied extensively, little is known about how plants adapt their growth under mild drought stress conditions. Here, we analyzed the leaf and rosette growth response of six Arabidopsis thaliana accessions originating from different geographic regions, when exposed to mild drought stress. The automated phenotyping platform WIWAM was used to impose stress early during leaf development, when the third leaf emerges from the shoot apical meristem. Analysis of growth related phenotypes showed differences in leaf development between the accessions. In all six accessions, mild drought stress reduced both leaf pavement cell area and number, without affecting the stomatal index. Genome-wide transcriptome analysis (using RNA sequencing) of early developing leaf tissue identified 354 genes differentially expressed under mild drought stress in the six accessions. Our results indicate the existence of a robust response over different genetic backgrounds to mild drought stress in developing leaves. The processes involved in the overall mild drought stress response comprised abscisic acid signaling, proline metabolism and cell wall adjustments. In addition to these known severe drought related responses, 87 genes were found to be specific for the response of young developing leaves to mild drought stress. Copyright © 2015, American Society of Plant Biologists.
    Plant physiology 01/2015; 167(3). DOI:10.1104/pp.114.254284 · 6.84 Impact Factor
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    • "Moreover, while overexpression ofAtGH3.5 increases level of IAA accumulation (Zhang et al. 2007), the gain-of-function mutant of AtGH3.5 also elevates SA accumulation and increases expression of PATHOGENESIS-RELATED PROTEIN 1 (PR-1) in response to biotic stress. While experiments with above mutants demonstrate that amino acid conjugates of SA by auxin upregulated GH3 proteins can act as a bioactive trigger of plant pathogen defense responses (Park et al. 2007). "
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    ABSTRACT: Plant hormones operate in a very complex network where they regulate and control different vital mechanisms. They coordinate growth, development and defense via signaling involving different interactions of molecules. Activation of molecules responsible for regulation of plant immunity is mainly provided by salicylic and jasmonic acid signaling pathways. Similar to the signaling of these defense-associated plant hormones, auxin can also affect resistance to different pathogen groups and disease is manifested indirectly through the effects on growth. The various ways in which auxin regulate growth and plant development and might be closely connected to plant defense, are discussed in this review.
    Biologia 10/2014; 69(10). DOI:10.2478/s11756-014-0431-3 · 0.83 Impact Factor
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    • "Depending on the type, intensity and duration of environmental stimuli as well as the plant developmental stage, auxin regulation could be controlled at different levels. For example, changes in auxin homeostasis and redistribution have been reported for plants growing under osmotic or mild salt stresses [2], [48], [49], [50]. When other ways by which NaCl might inhibit auxin response to salinity were explored, no difference in the concentration of free IAA was detected in WT seedlings under salt treatment (data not shown). "
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    ABSTRACT: One of the most striking aspects of plant plasticity is the modulation of development in response to environmental changes. Plant growth and development largely depend on the phytohormone auxin that exerts its function through a partially redundant family of F-box receptors, the TIR1-AFBs. We have previously reported that the Arabidopsis double mutant tir1 afb2 is more tolerant to salt stress than wild-type plants and we hypothesized that down-regulation of auxin signaling might be part of Arabidopsis acclimation to salinity. In this work, we show that NaCl-mediated salt stress induces miR393 expression by enhancing the transcription of AtMIR393A and leads to a concomitant reduction in the levels of the TIR1 and AFB2 receptors. Consequently, NaCl triggers stabilization of Aux/IAA repressors leading to down-regulation of auxin signaling. Further, we report that miR393 is likely involved in repression of lateral root (LR) initiation, emergence and elongation during salinity, since the mir393ab mutant shows reduced inhibition of emergent and mature LR number and length upon NaCl-treatment. Additionally, mir393ab mutant plants have increased levels of reactive oxygen species (ROS) in LRs, and reduced ascorbate peroxidase (APX) enzymatic activity compared with wild-type plants during salinity. Thus, miR393 regulation of the TIR1 and AFB2 receptors could be a critical checkpoint between auxin signaling and specfic redox-associated components in order to coordinate tissue and time-specific growth responses and tolerance during acclimation to salinity in Arabidopsis.
    PLoS ONE 09/2014; 9(9):e107678. DOI:10.1371/journal.pone.0107678 · 3.23 Impact Factor
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