An Aluminum-Activated Citrate Transporter in Barley

Research Institute for Bioresources, Okayama University, Chuo, Kurashiki, Okayama, 710-0046, Japan.
Plant and Cell Physiology (Impact Factor: 4.93). 09/2007; 48(8):1081-91. DOI: 10.1093/pcp/pcm091
Source: PubMed


Soluble ionic aluminum (Al) inhibits root growth and reduces crop production on acid soils. Al-resistant cultivars of barley (Hordeum vulgare L.) detoxify Al by secreting citrate from the roots, but the responsible gene has not been identified yet. Here, we identified a gene (HvAACT1) responsible for the Al-activated citrate secretion by fine mapping combined with microarray analysis, using an Al-resistant cultivar, Murasakimochi, and an Al-sensitive cultivar, Morex. This gene belongs to the multidrug and toxic compound extrusion (MATE) family and was constitutively expressed mainly in the roots of the Al-resistant barley cultivar. Heterologous expression of HvAACT1 in Xenopus oocytes showed efflux activity for (14)C-labeled citrate, but not for malate. Two-electrode voltage clamp analysis also showed transport activity of citrate in the HvAACT1-expressing oocytes in the presence of Al. Overexpression of this gene in tobacco enhanced citrate secretion and Al resistance compared with the wild-type plants. Transiently expressed green fluorescent protein-tagged HvAACT1 was localized at the plasma membrane of the onion epidermal cells, and immunostaining showed that HvAACT1 was localized in the epidermal cells of the barley root tips. A good correlation was found between the expression of HvAACT1 and citrate secretion in 10 barley cultivars differing in Al resistance. Taken together, our results demonstrate that HvAACT1 is an Al-activated citrate transporter responsible for Al resistance in barley.

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    • "But different from ALMT1, the transporters encoded belong to the multidrug and toxic compound extrusion (MATE) protein family. From this family, first Al-resistant genes HvAACT1 and SbMATE were isolated through the map-based cloning of the major Al-tolerant loci from barley (Furukawa et al. 2007) and sorghum (Magalhaes et al. 2007), respectively. Later on, MATE orthologs which are citrate transporter have been identified from Arabidopsis (AtMATE1; Liu et al. 2009), wheat (TaMATE; Ryan et al. 2009), maize (ZmMATE1; Maron et al. 2010), rye (ScMATE 2; Yokosho et al. 2010), and rice (OsFRDL2; "
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    ABSTRACT: Achieving sustainable food production to feed the increasing population of the problematic lands of the world is an enormous challenge. Aluminum (Al) toxicity in the acid soil is a major worldwide problem. Liming and nutrient management technologies are worthless due to high lime requirement, and the effect of liming does not persist for long. Besides this, conventional breeding is useful to manage Al toxicity as some plants have evolved mechanisms to cope with Al toxicity in acid soil. Therefore, understanding of Al tolerance mechanisms is prime necessity for improving Al tolerance in crops. Al resistance mechanisms include mainly Al avoidance (Al exclusion) and/or Al tolerance (detoxification of Al inside the cell) mechanisms. In this chapter, we summarize Al behavior in plant root cell. We include recent findings of Al resistance mechanisms and Al-resistant genes which can be useful to produce cultivars adapted to acid soils.
    Stress Responses in Plants, Edited by BN Tripathi and Maria Mueller, 07/2015; Springer.
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    • "The most-studied mechanism is the secretion of organic acid anions such as citrate, malate and oxalate from roots to chelate toxic Al ions in the rhizosphere (Delhaize et al. 1993; Ma et al. 1997, 2004a; Zhao et al. 2003). Recently, genes involved in the Al-induced secretion of malate and citrate have been identified in several plant species (Sasaki et al. 2004; Furukawa et al. 2007; Magalhaes et al. 2007). In addition, a number of other Al tolerance genes have also been identified especially in rice (Huang et al. 2009; Yamaji et al. 2009; Delhaize et al. 2012; Ma et al. 2014). "

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    • "A gene (ScALMT1), which is a homologue to wheat Ta- ALMT1 (Sasaki et al. 2004), has been implicated in Al-induced malate secretion in rye (Fontecha et al. 2007). Another gene (ScMATE1 = ScAACT1), which is a homologue of barley HvMATE1 (Furukawa et al. 2007) and also of wheat TaMATE1 (Ryan et al. 2009; Tovkach et al. 2013; Garc ıa-Oliveira et al. 2014), is involved in Al-induced citrate exudation in rye (Silva- Navas et al. 2012). The rye SOD genes have not been identified and the Alinduced changes in their mRNA expression have not yet been analysed. "
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    ABSTRACT: Aluminium (Al) is the main factor that limits crop production in acidic soils. There is evidence that antioxidant enzymes such as superoxide dismutase (SOD) play a key role against Al-induced oxidative stress in several plant species. Rye is one of the most Al-tolerant cereals and exudes both citrate and malate from the roots in response to Al. The role of SOD against Al-induced oxidative stress has not been studied in rye. Al accumulation, lipid peroxidation, H2O2 production and cell death were significantly higher in sensitive than in tolerant rye cultivars. Also, we characterised two genes for rye SOD: ScCu/ZnSOD and ScMnSOD. These genes were located on the chromosome arms of 2RS and 3RL, respectively, and their corresponding hypothetical proteins were putatively classified as cytosolic and mitochondrial, respectively. The phylogenetic relationships indicate that the two rye genes are orthologous to the corresponding genes of other Poaceae species. In addition, we studied Al-induced changes in the expression profiles of mRNAs from ScCu/ZnSOD and ScMnSOD in the roots and leaves of tolerant Petkus and sensitive Riodeva rye. These genes are mainly expressed in roots in both ryes, being induced by Al. The tolerant cultivar has more of both mRNAs than the sensitive line, indicating that roots of this tolerant rye are probably involved in Al tolerance.
    Plant Biology 10/2014; 17(3). DOI:10.1111/plb.12281 · 2.63 Impact Factor
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