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: 4.98). 09/2007; 48(8):1081-91. DOI: 10.1093/pcp/pcm091
Source: PubMed

ABSTRACT 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Background Aluminum (Al) toxicity has limited the productivity and expansion of cereal crops on acid soils; however, a number of plant species or cultivars have developed different strategies for detoxifying aluminum both internally and externally. Scope This review focuses on recent progress on molecular mechanisms of Al tolerance in gramineous plants. Conclusions A common mechanism in all gramineous plants is the secretion of organic acid anions (citrate and malate) from the roots. Genes belonging to ALMT (for Aluminum-activated malate transporter) and MATE (Multidrug and toxic compound extrusion) family involved in the secretion have been identified in several plant species; however, different plant species show different gene expression patterns including Al-induction, spatial and temporal expression, and tissue localization. Furthermore, the mechanisms regulating the gene expression also differ with plant species, which are achieved by increased tandem repeated element, increase of copy number, insertion of transposon, or alteration of cis-acting element. In addition to these common Al exclusion mechanisms, rice as a highly Al-tolerant species has developed a number of other mechanisms for detoxification of Al. A transcription factor for Al tolerance ART1 identified in rice regulates at least 30 genes implicated in internal and external detoxification of Al. These multiple genes may contribute to the high Al tolerance of rice. In the future, regulation mechanisms of Al-tolerance genes need to be further investigated.
    Plant and Soil 08/2014; 381(1-2):1-12. DOI:10.1007/s11104-014-2073-1 · 3.24 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Similar to common buckwheat (Fagopyrum esculentum), tartary buckwheat (Fagopyrum tataricum) shows a high level of aluminum (Al) tolerance and accumulation. However, the molecular mechanisms for Al detoxification and accumulation are still poorly understood. To begin to elucidate the molecular basis of Al tolerance and accumulation, we used the Illumina high-throughput mRNA sequencing (RNA-seq) technology to conduct a genome-wide transcriptome analysis on both tip and basal segments of the roots exposed to Al.ResultsBy using the Trinity method for the de novo assembly and cap3 software to reduce the redundancy and chimeras of the transcripts, we constructed 39,815 transcripts with an average length of 1184 bp, among which 20,605 transcripts were annotated by BLAST searches in the NCBI non-redundant protein database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that expression of genes involved in the defense of cell wall toxicity and oxidative stress was preferentially induced by Al stress. Our RNA-seq data also revealed that organic acid metabolism was unlikely to be a rate-limiting step for the Al-induced secretion of organic acids in buckwheat. We identified two citrate transporter genes that were highly induced by Al and potentially involved in the release of citrate into the xylem. In addition, three of four conserved Al-tolerance genes were found to be duplicated in tartary buckwheat and display diverse expression patterns.Conclusions Nearly 40,000 high quality transcript contigs were de novo assembled for tartary buckwheat, providing a reference platform for future research work in this plant species. Our differential expression and phylogenetic analysis revealed novel aspects of Al-tolerant mechanisms in buckwheat.
    BMC Plant Biology 01/2015; 15(1):16. DOI:10.1186/s12870-014-0395-z · 3.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A previously-identified Arabidopsis mutant with hypersensitivity to aluminum, als7-1 was studied further to determine the nature of the mutation and subsequently establish the biochemical basis of the increase in Al sensitivity. Physiological analysis revealed that the Al hypersensitivity phenotype is correlated with increased Al uptake and Al-dependent gene expression, indicating that als7-1 has a defect in an Al-exclusion mechanism. Cloning of the als7-1 mutation showed that it negatively affects the gene encoding the putative nucleolar localised ribosomal biogenesis factor SLOW WALKER2, which is required for normal gametogenesis and mitotic progression. Molecular analysis indicated that Al hypersensitivity in als7-1 is correlated with loss of expression of a factor required for S-adenosylmethionine recycling and reduced levels of endogenous polyamines in the mutant. Further analysis shows that Al-dependent root growth inhibition is reversed by addition of exogenous spermine, which is correlated with a significant reduction in Al uptake by spermine treated roots. Endogenous spermine likely functions to compete with Al3+ for binding to extra- and intracellular anionic sites, which suggests that increased spermine levels may be an effective means to improve root growth in Al toxic acid soil environments.
    Functional Plant Biology 01/2013; 40(1):67. DOI:10.1071/FP12234 · 2.57 Impact Factor

Full-text (2 Sources)

Available from
May 27, 2014