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Sete Lagoas, Brazil

Zhou G.,University of Tasmania | Zhou G.,CSIRO | Pereira J.F.,Embrapa Wheat | Delhaize E.,CSIRO | And 3 more authors.
Journal of Experimental Botany | Year: 2014

Malate and citrate efflux from root apices is a mechanism of Al 3+ tolerance in many plant species. Citrate efflux is facilitated by members of the MATE (multidrug and toxic compound exudation) family localized to the plasma membrane of root cells. Barley (Hordeum vulgare) is among the most Al3+-sensitive cereal species but the small genotypic variation in tolerance that is present is correlated with citrate efflux via a MATE transporter named HvAACT1. This study used a biotechnological approach to increase the Al3+ tolerance of barley by transforming it with two MATE genes that encode citrate transporters: SbMATE is the major Al 3+-tolerance gene from sorghum whereas FRD3 is involved with Fe nutrition in Arabidopsis. Independent transgenic and null T3 lines were generated for both transgenes. Lines expressing SbMATE showed Al 3+-activated citrate efflux from root apices and greater tolerance to Al3+ toxicity than nulls in hydroponic and short-term soil trials. Transgenic lines expressing FRD3 exhibited similar phenotypes except citrate release from roots occurred constitutively. The Al3+ tolerance of these lines was compared with previously generated transgenic barley lines overexpressing the endogenous HvAACT1 gene and the TaALMT1 gene from wheat. Barley lines expressing TaALMT1 showed significantly greater Al3+ tolerance than all lines expressing MATE genes. This study highlights the relative efficacy of different organic anion transport proteins for increasing the Al3+ tolerance of an important crop species. © 2014 The Author.

Kochian L.V.,Cornell University | Pineros M.A.,Cornell University | Liu J.,Cornell University | Magalhaes J.V.,Embrapa Maize and Sorghum
Annual Review of Plant Biology | Year: 2015

Aluminum (Al) toxicity in acid soils is a significant limitation to crop production worldwide, as approximately 50 of the world's potentially arable soil is acidic. Because acid soils are such an important constraint to agriculture, understanding the mechanisms and genes conferring resistance to Al toxicity has been a focus of intense research interest in the decade since the last article on crop acid soil tolerance was published in this journal. An impressive amount of progress has been made during that time that has greatly increased our understanding of the diversity of Al resistance genes and mechanisms, how resistance gene expression is regulated and triggered by Al and Al-induced signals, and how the proteins encoded by these genes function and are regulated. This review examines the state of our understanding of the physiological, genetic, and molecular bases for crop Al tolerance, looking at the novel Al resistance genes and mechanisms that have been identified over the past ten years. Additionally, it examines how the integration of molecular and genetic analyses of crop Al resistance is starting to be exploited for the improvement of crop plants grown on acid soils via both molecular-assisted breeding and biotechnology approaches. ©2015 by Annual Reviews. All rights reserved.

Liu J.,Cornell University | Luo X.,Cornell University | Luo X.,Southwest University | Shaff J.,Cornell University | And 7 more authors.
Plant Journal | Year: 2012

The primary mechanism of Arabidopsis aluminum (Al) resistance is based on root Al exclusion, resulting from Al-activated root exudation of the Al 3+-chelating organic acids, malate and citrate. Root malate exudation is the major contributor to Arabidopsis Al resistance, and is conferred by expression of AtALMT1, which encodes the root malate transporter. Root citrate exudation plays a smaller but still significant role in Arabidopsis Al resistance, and is conferred by expression of AtMATE, which encodes the root citrate transporter. In this study, we demonstrate that levels of Al-activated root organic acid exudation are closely correlated with expression of the organic acid transporter genes AtALMT1 and AtMATE. We also found that the AtALMT1 promoter confers a significantly higher level of gene expression than the AtMATE promoter. Analysis of AtALMT1 and AtMATE tissue- and cell-specific expression based on stable expression of promoter-reporter gene constructs showed that the two genes are expressed in complementary root regions: AtALMT1 is expressed in the root apices, while AtMATE is expressed in the mature portions of the roots. As citrate is a much more effective chelator of Al 3+ than malate, we used a promoter-swap strategy to test whether root tip-localized expression of the AtMATE coding region driven by the stronger AtALMT1 promoter (AtALMT1P::AtMATE) resulted in increased Arabidopsis Al resistance. Our results indicate that expression of AtALMT1 P::AtMATE not only significantly increased Al resistance of the transgenic plants, but also enhanced carbon-use efficiency for Al resistance. © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.

Background: Aluminium (Al) toxicity is a major agricultural constraint for crop cultivation on acid soils, which comprise a large portion of the world's arable land. One of the most widely accepted mechanisms of Al tolerance in plants is based on Al-activated organic acid release into the rhizosphere, with organic acids forming stable, non-toxic complexes with Al. This mechanism has recently been validated by the isolation of bona-fide Al-tolerance genes in crop species, which encode membrane transporters that mediate Al-activated organic acid release leading to Al exclusion from root apices. In crop species such as sorghum and barley, members in the multidrug and toxic compound extrusion (MATE) family underlie Al tolerance by a mechanism based on Al-activated citrate release. Scope and Conclusions: The study of Al tolerance in plants as conferred by MATE family members is in its infancy. Therefore, much is yet to be discovered about the functional diversity and evolutionary dynamics that led MATE proteins to acquire transport properties conducive to Al tolerance in plants. In this paper we review the major characteristics of transporters in the MATE family and will relate this knowledge to Al tolerance in plants. The MATE family is clearly extremely flexible with respect to substrate specificity, which raises the possibility that Al tolerance as encoded by MATE proteins may not be restricted to Al-activated citrate release in plant species. There are also indications that regulatory loci may be of pivotal importance to fully explore the potential for Al-tolerance improvement based on MATE genes. © The Author 2010.

Martins B.A.B.,Embrapa Maize and Sorghum | Christoffoleti P.J.,University of Sao Paulo
Scientia Agricola | Year: 2015

Knowledge of the effects of seed burial depth and the presence of straw on the soil surface on weed seedling emergence provides useful information for the development of weed management tactics. Buttonweed (Borreria densiflora DC.) is a troublesome weed that occurs in large infestations in soybean and sugarcane crops from north-central Brazil. This study investigated buttonweed emergence at different seed burial depths and straw amounts present on the soil surface. The experiment was conducted in greenhouse conditions, under a factorial design between four seed burial depths and four amounts of surface straw. Percent seedling emergence and fresh biomass (g) were evaluated at twenty-five days after installation (DAI). Greater buttonweed emergence occurred in seeds that were placed on the soil surface either without surface straw or with up to 1,000 kg ha−1 of straw on the soil surface. With 4,000 kg ha−1 of surface straw, buttonweed emergence was prevented when seeds were placed at a depth of 0.5 cm or deeper in the soil. These data indicated emergence of this weed species was greater at depths near the soil surface and in soils with the least amounts of surface straw. Information generated in this study provides a starting point for the development of knowledge for understanding the biology of buttonweed emergence and its population dynamics. Such information may be directly transmitted to growers and lays the groundwork for an integrated management approach for this weed species. © 2015, Scientia Agricola , All rights reserved.

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