Analysis of gene expression in poplar trees (Populus deltoides x nigra, DN34) exposed to the toxic explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).

Poplar plants (Populus deltoides x nigra, DN34) growing under hydroponic conditions were exposed to 50 mg L(-1) of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) for 24 h. The expression of genes potentially involved in the metabolism of toxic explosives was analyzed by reverse-transcriptase (RT) real-time PCR. Genes under study were selected by reference to corresponding genes that were previously shown to be upregulated in the model plant Arabidopsis thaliana by exposure to 2,4,6-trinitrotoluene (TNT) (Ekman et al., 2003. Plant Physiol., 133, 1397-1406). The target genes investigated include several genes encoding for enzymes known to be involved in the detoxification of xenobiotic pollutants, such as glutathione S-transferases (GSTs), cytochrome P-450s (CYPs), NADPH-dependent reductases, and peroxidases. Starting from A. thaliana TNT-inducible genes, corresponding Populus sequences were retrieved from the JGI Poplar Genome Project database and were used to design gene-specific primers. 18S ribosomal DNA (rDNA) was used as an internal standard and recorded gene expression levels were normalized by reference to nonexposed plants. In three separate experiments, five genes were found to be significantly amplified in leaf tissues by exposure to RDX, including GST (9.7 fold), CYP (1.6 fold), reductases (1.6-1.7 fold), and peroxidase (1.7 fold). In root tissues, only a single GST gene was found to be significantly amplified by exposure to RDX (2.0 fold). These results show, for the first time, that the exposure of poplar plants to RDX results in the induction of several genes that are potentially involved in explosive detoxification.