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 StatesJournal of Biological Chemistry (Impact Factor: 4.57). 04/2007; 282(13):10036-46. DOI: 10.1074/jbc.M610524200
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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- "es et al . 4 factor , MYB96 , regulates drought stress responses by integrating ABA and auxin signals in seed germina - tion . During both germination and seedling growth , endogenous IAA levels were unaltered in the myb96 - ox mutant , which would be due to rigorous control of auxin homeostasis under stress conditions ( Dombrecht et al . , 2007 ; Park et al . , 2007 ) . Similarly , Jung and Park ( 2011 ) demonstrated that seed germination in Arabidopsis is suppressed by auxin under high salinity ( 150 mM NaCl ) . These authors generated transgenic plants overexpressing the YUCCA3 ( YUC3 ) gene , which encodes an auxin biosynthetic enzyme ( Zhao et al . , 2001 ) . Seed germination of the YUC3 - over"
ABSTRACT: The most critical phase in plant life is seed germination, which is influenced by environmental factors. Drought and salinity are key environmental factors that affect seed germination. Reduction or alterations of germination when seeds are exposed to these factors have been shown to be due to either the adverse effects of water limitation and/or specific ion toxicity on metabolism. Phytohormones are chemical messengers produced within the plant that control its growth and development in response to environmental cues; small fluctuations of phytohormone levels alter the cellular dynamics and, hence, play a central role in regulating plant growth responses to these environmental factors. To integrate current knowledge, the present review focuses on the involvement of endogenous phytohormones in plant adaptative responses to drought and salinity at one of the plant's developmental phases.
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- "To test this hypothesis two distinct environmental growth perturbations were chosen to investigate their effect on IAA homeostasis mediated by the GH3 family in P. patens based on previous reports that IAA and its conjugates could be connected. (a) Elevated temperatures because it was shown that they were related to increased auxin in two different plant species (Oetiker and Aeschbacher, 1997; Gray et al., 1998), and because gh3.5 mutants of Arabidopsis were more susceptible to elevated temperatures (Park et al., 2007a). (b) Darkness, because another Arabidopsis GH3 gene was involved in light-dependent growth. "
ABSTRACT: Two proteins of the GRETCHEN HAGEN3 (GH3) family of acyl acid amido synthetases from the moss Physcomitrella patens conjugate indole-3-acetic acid (IAA) to a series of amino acids. The possible function of altered auxin levels in the moss in response to two different growth perturbations, elevated temperatures and darkness, was analyzed using a) the recently described double knockout lines in both P. patens GH3 genes (GH3-doKO) and b) a previously characterized line harboring an auxin-inducible soybean GH3 promoter::reporter fused to β-glucuronidase (G1-GUS). The GUS activity as marker of the auxin response increased at higher temperatures and after cultivation in the darkness for a period of up to four weeks. Generally, the double knockout plants grew more slowly than the wild type (WT). The altered growth conditions influenced the phenotypes of the double knockout lines differently from that of WT moss. Higher temperatures negatively affected GH3-doKO plants compared to WT which was shown by stronger loss of chlorophyll. On the other hand, a positive effect was found on the concentrations of free IAA which increased at 28 °C in the GH3-doKO lines compared to WT plants. A different factor, namely darkness vs. a light/dark cycle caused the adverse phenotype concerning chlorophyll concentrations. Mutant moss plants showed higher chlorophyll concentrations than WT and these correlated with higher free IAA in the plant population that was classified as green. Our data show that growth perturbations result in higher free IAA levels in the GH3-doKO mutants, but in one case - growth in darkness - the mutants could cope better with the condition, whereas at elevated temperatures the mutants were more sensitive than WT. Thus, GH3 function in P. patens WT could lie in the regulation of IAA concentrations under unfavorable environmental conditions.
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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. "
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.
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