An Aluminum-Activated Citrate Transporter in Barley

Okayama University, Okayama, Okayama, 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 14C-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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Available from: Yoshiko Murata
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    • "Multidrug and Toxic Compound Extrusion (MATE) families were cloned in wheat (TaALMT1) (Sasaki et al. 2004), sorghum (SbMATE) (Magalhaes et al. 2007) and barley (HvAACT1) (Furukawa et al. 2007) via hydroponic-based assessments of Al tolerance. "
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    ABSTRACT: Aluminum (Al) toxicity damages plant roots and limits crop production on acid soils that comprise up to 50% of the world's arable lands. A major Al tolerance locus on chromosome 3, AltSB, controls aluminum tolerance in sorghum [Sorghum bicolor (L.) Moench] via SbMATE, an Al-activated plasma membrane transporter that mediates Al exclusion from sensitive regions in the root apex. SbMATE, as is the case of other known Al tolerance genes, was cloned based on studies conducted under controlled environmental conditions, in nutrient solution. Therefore, its impact on grain yield on acid soils remains undetermined. To determine SbMATE's real world impact, multi-trait QTL mapping in hydroponics and in the field revealed a large-effect QTL colocalized with the Al tolerance locus, AltSB where SbMATE lies, conferring a 0.6 ton ha-1 grain yield increase on acid soils. A second QTL for Al tolerance in hydroponics, where the positive allele was also donated by the Al tolerant parent, SC283, was found on chromosome 9, indicating the presence of distinct Al tolerance genes in the sorghum genome or genes acting in the SbMATE pathway leading to Al-activated citrate release. There was no yield penalty for AltSB, consistent with the highly localized Al regulated SbMATE expression in the root tip and Al-dependent transport activity. A female effect of 0.5 ton ha-1 independently demonstrated the effectiveness of AltSB in hybrids. Al tolerance conferred by AltSB is thus an indispensable asset for sorghum production and food security on acid soils, many of which are located in developing countries.
    Full-text · Article · Dec 2015 · G3-Genes Genomes Genetics
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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.
    Full-text · Chapter · Jul 2015
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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). "

    Full-text · Dataset · Jun 2015
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