Högskolan i Skövde

Previously, our in silico analyses identified four candidate genes that might be involved in uptake and/or accumulation of arsenics in plants: arsenate reductase 2 (ACR2), phytochelatin synthase 1 (PCS1) and two multi-drug resistant proteins (MRP1 and MRP2) [Lund et al. (2010) J Biol Syst 18:223–224]. We also postulated that one of these four genes, ACR2, seems to play a central role in this process. To investigate further, we have constructed a 3D structure of the Arabidopsis thaliana ACR2 protein using the iterative implementation of the threading assembly refinement (I-TASSER) server. These analyses revealed that, for catalytic metabolism of arsenate, the arsenate binding-loop (AB-loop) and residues Phe-53, Phe-54, Cys-134, Cys-136, Cys-141, Cys-145, and Lys-135 are essential for reducing arsenate to arsenic intermediates (arsenylated enzyme-substrate intermediates) and arsenite in plants. Thus, functional predictions suggest that the ACR2 protein is involved in the conversion of arsenate to arsenite in plant cells. To validate the in silico results, we exposed a transfer-DNA (T-DNA)-tagged mutant of A. thaliana (mutation in the ACR2 gene) to various amounts of arsenic. Reverse transcriptase PCR revealed that the mutant exhibits significantly reduced expression of the ACR2 gene. Spectrophotometric analyses revealed that the amount of accumulated arsenic compounds in this mutant was approximately six times higher than that observed in control plants. The results obtained from in silico analyses are in complete agreement with those obtained in laboratory experiments.