A comparison of promoters for expression of transgenes in alfalfa roots
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Aluminum toxicity in acid soils poses a serious limitation to production crops including alfalfa. Transgenic approaches have been employed in a number of studies, which focused on the overexpression of genes associated with either organic acid synthesis or transportation. The success of a transgenic project depends on the use of the proper promoter. In this study, a gene coding citrate synthase and a gene coding for DcPA1 were engineered into alfalfa, each driven by one of three different promoters: the constitutive MtHP, the root-specific MtPT1and the root-specific ROC gene complex, to compare the effectiveness of these promoters to drive traits associated with aluminum tolerance. The promoter MtHP and ROC system provided significantly higher citrate production in roots of transgenic alfalfa, relative to the controls, while no significant difference in citrate levels was observed when MtPT1 was used as a promoter. Citrate concentration in roots of the best event was 2.81 mg g-1 which was 2.5-fold greater than that of wild-type alfalfa genotype R2336. Similar patterns were observed for the expression of DcPA1 gene. Overall, the results suggest that the MtHP promoter is the best candidate to use in alfalfa in order to enhance alfalfa aluminum tolerance through genetic engineering approaches.