Identification of transcription factors involved in root apex responses to salt stress in Medicago truncatula. Mol Genet Genom

Institut des Sciences du Végétal, C.N.R.S., 91198, Gif-sur-Yvette, France.
Molecular Genetics and Genomics (Impact Factor: 2.73). 12/2008; 281(1):55-66. DOI: 10.1007/s00438-008-0392-8
Source: PubMed


The root apex contains meristematic cells that determine root growth and architecture in the soil. Specific transcription factor (TF) genes in this region may integrate endogenous signals and external cues to achieve this. Early changes in transcriptional responses involving TF genes after a salt stress in Medicago truncatula (Mt) roots were analysed using two complementary transcriptomic approaches. Forty-six salt-regulated TF genes were identified using massive quantitative real-time RT-PCR TF profiling in whole roots. In parallel, Mt16K+ microarray analysis revealed 824 genes (including 84 TF sequences) showing significant changes (p < 0.001) in their expression in root apexes after a salt stress. Analysis of salt-stress regulation in root apexes versus whole roots showed that several TF genes have more than 30-fold expression differences including specific members of AP2/EREBP, HD-ZIP, and MYB TF families. Several salt-induced TF genes also respond to other abiotic stresses as osmotic stress, cold and heat, suggesting that they participate in a general stress response. Our work suggests that spatial differences of TF gene regulation by environmental stresses in various root regions may be crucial for the adaptation of their growth to specific soil environments.

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    • "Many TFs have been reported to regulate the response to drought and salt stress in M. truncatula at the transcriptional level. Microarray Mt16K+ showed that the expression of WRKY TFs changed significantly in root apexes under 100 mM NaCl stress (Gruber et al., 2009). MtNAC969 was induced by abiotic stresses (salt, drought and cold), and shown to increase the tolerance to high salinity (de Zelicourt et al., 2012). "
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    ABSTRACT: WRKY transcription factors have been studied in a wide range of plant species, but have remained largely uncharacterized in legumes. To obtain insight into the functions of WRKY in legumes, we isolated and characterized one WRKY family member from Medicago truncatula, MtWRKY76, which belongs to sub-group II.Expression analysis showed that MtWRKY76 was rapidly induced by abiotic stresses. MtWRKY76 overexpression markedly enhanced the salt and drought tolerance of transgenic M. truncatula and triggered abiotic inducible genes. MtWRKY76 was located in the nucleus and interacted with Medtr1g098680.1 that was deduced as ASR protein, which acted as a component of a transcription-regulating complex involved in abiotic stress signalling pathways. Interestingly, MtWRKY76 was found to be involved in regulated abiotic pathways via Solexa/Illumina digital gene expression (DGE) analysis.In conclusion, we demonstrated that MtWRKY76 was a multifunctional abiotic stress response gene in M. truncatula.
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    • "In a parallel study, transcriptome analysis based on the 16K+ microarrays (Mt16KOLI1) using salttreated root apexes was performed in the model legume M. truncatula (Gruber et al., 2009) comparing the salt tolerant TN1.11 variety and the reference Jemalong A17 genotype. The hormonal response to salt stress of M. truncatula roots was monitored in different tissues (roots, stem and leaves) at different time point from stress onset. "
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    • "M. truncatula is also an interesting model for analysing responses to salt stress. These responses have been studied at different levels from whole-plant to molecular analysis (Veatch et al. 2004; López et al. 2008a, 2008b de Lorenzo et al. 2009; Li et al. 2009 Li et al. , 2011 Merchan et al. 2007; Ariel et al. 2010; Gruber et al. 2009; Arraouadi et al. 2011 Arraouadi et al. , 2012) and several genes that are putatively involved in different mechanisms of tolerance to salt stress have been reported (Gruber et al. 2009; Zahaf et al. 2012). In addition, the natural diversity of M. truncatula with respect to salt stress has been characterised. "
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    ABSTRACT: Salinity is one of the major stresses that limits crop production worldwide and affects most physiological activities in plants. In order to study the genetic control of salt stress in the model legume Medicago truncatula Gaertn., an experiment was undertaken to determine the genetic variability and to identify quantitative trait loci (QTLs) controlling several traits related to plant growth and physiology in a population of recombinant inbred lines. Shoot and rootDW,relative water content, leaf area, chlorophyll content, chlorophyll fluorescence parameters, and Na+ and K+ in shoots and roots were measured. The experiment was carried out with three replications. ANOVA showed a large genetic variation and transgressive segregation for the traits studied, suggesting putative complex tolerance mechanisms. A total of 21 QTLs were detected under control conditions and 19 QTLs were identified under 100mM salt stress conditions, with three QTLs being common to both situations. The percentage of total phenotypic variance explained by the QTLs ranged from 4.6% to 23.01%. Overlapping QTLs for different traits were also observed, which enables us to discriminate independent traits from linked ones. The results should be helpful information for further functional analysis of salt tolerance in M. truncatula.
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