Molecular mechanisms of Al tolerance in gramineous plants

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 Alinduction, 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.

Early Seedling Growth as a Tool to Assess the Tolerance of Urochloa brizantha Cultivars to Free Aluminium

“…Aluminium resistance can be split in two sub-mechanisms: a) aluminium avoidance: the plant leaks organic acids (citrate, malate, or oxalate) into the rhizosphere, preventing the Al 3+ from reaching the root tips, and keeping it as a chelate (Delhaize et al, 1993a(Delhaize et al, , 1993bMa et al, 2001Ma et al, , 2014; and b) aluminium tolerance: which means that the plant may accumulate the element in the exodermis cell walls (Arroyale et al, 2011(Arroyale et al, , 2013, or take up aluminium and immobilize it in the vacuoles. In gramineous crops of commercial importance, including some Triticinae (Delhaize et al, 1993a(Delhaize et al, , 1993bMa et al, 2001Ma et al, , 2014, maize (Giannakoula et al, 2010), and rice (Kikui et al, 2005;Roselló et al, 2015), this phenomenon is very well studied.…”

“…Tolerance/resistance to aluminium may be achieved by either exudation of organic ions (Delhaize et al, 1993a, b;Silva et al, 2013;Ma et al, 2014;Roselló et al, 2015;Ahmed et al, 2016;Chen & Liao 2016) or by excluding the aluminium from the roots in the outer layers of the exodermis (Arroyave et al, 2011(Arroyave et al, , 2013. Aluminium causes oxidative stress in plants, leading some species to increase the activities of antioxidant enzymes (Giannakoula et al, 2010;Silva, 2012).…”

Transgene Insertion Stability and Aluminum Tolerance Candidate Gene Expression in T3 Generation of Transgenic Tobacco

“…The ALMT1 gene was also highly expressed in the transgenic line under Al stress compared to both wild type and unstressed transgenic line, suggesting that the ALMT1 gene also involved in Al tolerance. The ALMT1 was reported to contribute to Al detoxification in several plants species (Ma et al, 2014). ALMT1 is a gene encoding malate transporter that responsible for malate secretion.…”

Differences in Aluminium Accumulation and Resistance between Genotypes of the Genus Fagopyrum

“…Less binding of Al in the cell walls owing to a lower content of unmethylated pectins [10,11] or hemicellulose [12] of the cell wall may also contribute to Al exclusion. There is recent evidence that both Al exclusion and Al tolerance contribute to Al resistance in a coordinated way in Arabidopsis [13] and particularly in the Al-resistant cereal crop rice [14]. In some plant species Al tolerance is combined with the capacity to translocate Al to the shoots where Al is accumulated in large concentrations in the leaves [15,16].…”

“…Whereas the physiological and molecular understanding of resistance mechanisms in Al-excluding plant species has made considerable progress in recent years [7,14,17], the understanding of Al accumulation in relation to Al tolerance still widely lags behind. The Al accumulator buckwheat is characterized by both, Al exclusion from uptake through Al-induced release by root tips of oxalate [18] and symplastic sequestration of Al by oxalate [19].…”