Molecular characterization of the citrate transporter gene TaMATE1 and expression analysis of upstream genes involved in organic acid transport under Al stress in bread wheat (Triticum aestivum)

Abstract

In bread wheat, besides malate, the importance of citrate efflux for Al tolerancehas also been reported. For better understanding the Al tolerance mechanismin bread wheat, here, we performed both a molecular characterization of thecitrate transporter gene TaMATE1 and an investigation on the upstream vari-ations in citrate and malate transporter genes. TaMATE1 belong to multidrugtransporter protein family, which are located on the long arm of homoeologousgroup 4 chromosomes (TaMATE1-4A, TaMATE1-4B TaMATE1-4D). TaMATE1homoeologues transcript expression study exhibited the preponderance ofhomoeologue TaMATE1-4B followed by TaMATE1-4D whereas homoeologueTaMATE1-4A seemed to be silenced. TaMATE1, particularly homoeologueTaMATE1-4B and TaALMT1 transcripts were much more expressed in the rootapices than in shoots of Al tolerant genotype Barbela 7/72/92 under both con-trol and Al stress conditions. In addition, in both tissues of Barbela 7/72/92,higher basal levels of these gene transcripts were observed than in Anahuac(Al sensitive). Noticeably, the presence of a transposon in the upstream ofTaMATE1-4B in Barbela 7/72/92 seems to be responsible for its higher tran-script expression where it may confer citrate efflux. Thus, promoter variations(transposon in TaMATE1-4B upstream and type VI promoter in TaALMT1) asso-ciated with higher basal transcript expression of TaMATE1-4B and TaALMT1clearly show how different mechanisms for Al tolerance operate simultane-ously in a single genotype. In conclusion, our results demonstrate that Barbela7/72/92 has favorable alleles for these organic acids transporter genes whichcould be utilized through genomic assisted selection to develop improvedcultivars for acidic soils.Abbreviations – 2D, two-dimensional; AACT, aluminum-activated citrate transporter; ALMT, Al-activated malate transporter;dNTP, deoxyribonucleotide triphosphates; EST, expressed sequence tag; MATE, multidrug and toxic compound exudation;OAs, organic acids; PCR, polymerase chain reaction; RT, reverse transcription; STOP, sensitive to proton rhizotoxicity.Physiol. Plant. 152, 2014 441