Selection and Breeding for Acid-Soil Tolerance in Crops

Koyama

Proc. Natl. Acad. Sci. U.S.A.

et al. 2007

365

366

Acid soil syndrome causes severe yield losses in various crop plants because of the rhizotoxicities of ions, such as aluminum (Al 3؉ ). Although protons (H ؉ ) could be also major rhizotoxicants in some soil types, molecular mechanisms of their tolerance have not been identified yet. One mutant that was hypersensitive to H ؉ rhizotoxicity was isolated from ethyl methanesulfonate mutagenized seeds, and a single recessive mutation was found on chromosome 1. Positional cloning followed by genomic sequence analysis revealed that a missense mutation in the zinc finger domain in a predicted Cys2His2-type zinc finger protein, namely sensitive to proton rhizotoxicity (STOP)1, is the cause of hypersensitivity to H ؉ rhizotoxicity. The STOP1 protein belongs to a functionally unidentified subfamily of zinc finger proteins, which consists of two members in Arabidopsis based on a Blast search. The stop1 mutation resulted in no effects on cadmium, copper, lanthanum, manganese and sodium chloride sensitivitities, whereas it caused hypersensitivity to Al 3؉ rhizotoxicity. This stop1 mutant lacked the induction of the AtALMT1 gene encoding a malate transporter, which is concomitant with Al-induced malate exudation. There was no induction of AtALMT1 by Al 3؉ treatment in the stop1 mutant. These results indicate that STOP1 plays a critical role in Arabidopsis tolerance to major stress factors in acid soils. aluminum toxicity ͉ Arabidopsis thaliana ͉ Cys2His2-type zinc finger protein ͉ proton-rhizotoxicity ͉ sensitive to proton rhizotoxicity

Section: Discussionmentioning

confidence: 99%

Zinc finger protein STOP1 is critical for proton tolerance in Arabidopsis and coregulates a key gene in aluminum tolerance

Koyama

Proc. Natl. Acad. Sci. U.S.A.

et al. 2007

365

366

“…In acid mineral soils, a variety of individual chemical constraints and interactions among them limit plant growth. For example, in low pH soils, it is not usually hydrogen ion toxicity which affects plant growth but rather other toxicities, such as aluminium (Al) and manganese, and deficiencies of phosphorus, nitrogen, potassium, calcium, magnesium, and molybdenum (Rao et al 1993). Aluminium toxicity is particularly severe at soil pH values of ≤5.0 (Foy 1974).…”

Section: Introductionmentioning

confidence: 99%

Interaction of aluminium and drought stress on root growth and crop yield on acid soils

2013

Background Aluminium (Al) toxicity and drought stress are two major constraints for crop production in the world, particularly in the tropics. The variation in rainfall distribution and longer dry spells in much of the tropics during the main growing period of crops are becoming increasingly important yield-limiting factors with the global climate change. As a result, crop genotypes that are tolerant of both drought and Al toxicity need to be developed. Scope The present review mainly focuses on the interaction of Al and drought on root development, crop growth and yield on acid soils. It summarizes evidence from our own studies and other published/related work, and provides novel insights into the breeding for the adaptation to these combined abiotic stresses. The primary symptom of Al phytotoxicity is the inhibition of root growth. The impeded root system will restrict the roots for exploring the acid subsoil to absorb water and nutrients which is particularly important under condition of low soil moisture in the surface soil under drought. Whereas drought primarily affects shoot growth, effects of phytotoxic Al on shoot growth are mostly secondary effects that are induced by Al affecting root growth and function, while under drought stress root growth may even be promoted. Much progress has recently been made in the understanding of the physiology and molecular biology of the interaction between Al toxicity and drought stress in common bean (Phaseolus vulgaris L.) in hydroponics and in an Al-toxic soil. Conclusions Crops growing on acid soils yield less than their potential because of the poorly developed root system that limits nutrient and water uptake. Breeding for drought resistance must be combined with Al resistance, to assure that drought resistance is expressed adequately in crops grown on soils with acid Al-toxic subsoils.

Proc. Natl. Acad. Sci. U.S.A.

“…In addition, in developed countries, high-input farming practices, including the excessive use of ammonia fertilizers, acidify previously neutral soils (3). Although chemical amendments such as lime can neutralize soil acidity, this option is not economically feasible for poor farmers, nor is it an effective strategy for alleviating subsoil acidity (4).…”

mentioning

confidence: 99%

AtALMT1 , which encodes a malate transporter, is identified as one of several genes critical for aluminum tolerance in Arabidopsis

Hoekenga

Maron

Piñeros

et al. 2006

502

513

Aluminum (Al) tolerance in Arabidopsis is a genetically complex trait, yet it is mediated by a single physiological mechanism based on Al-activated root malate efflux. We investigated a possible molecular determinant for Al tolerance involving a homolog of the wheat Al-activated malate transporter, ALMT1. This gene, named AtALMT1 (At1g08430), was the best candidate from the 14-member AtALMT family to be involved with Al tolerance based on expression patterns and genomic location. Physiological analysis of a transferred DNA knockout mutant for AtALMT1 as well as electrophysiological examination of the protein expressed in Xenopus oocytes showed that AtALMT1 is critical for Arabidopsis Al tolerance and encodes the Al-activated root malate efflux transporter associated with tolerance. However, gene expression and sequence analysis of AtALMT1 alleles from tolerant Columbia (Col), sensitive Landsberg erecta (Ler), and other ecotypes that varied in Al tolerance suggested that variation observed at AtALMT1 is not correlated with the differences observed in Al tolerance among these ecotypes. Genetic complementation experiments indicated that the Ler allele of AtALMT1 is equally effective as the Col allele in conferring Al tolerance and Al-activated malate release. Finally, fine-scale mapping of a quantitative trait locus (QTL) for Al tolerance on chromosome 1 indicated that AtALMT1 is located proximal to this QTL. These results indicate that AtALMT1 is an essential factor for Al tolerance in Arabidopsis but does not represent the major Al tolerance QTL also found on chromosome 1. abiotic stress ͉ electrophysiology ͉ genetics ͉ organic acid exudation