Transcriptional profiling of Arabidopsis seedlings in response to heavy metal lead (Pb)

Lead (Pb) is one of the main sources of pollution in the environment, and is severely toxic to plants and animals. Using a DNA microarray, the transcriptional profiles of Arabidopsis thaliana genes in response to Pb treatment were investigated under different concentrations of Pb(NO3)2 solution from low (1 μM, 10 μM) to high (100 μM) during the early stages of toxicity (3 h and 24 h). At each time point, Pb content was measured to confirm that the extensive heavy metal accumulation in Arabidopsis seedlings was caused by Pb treatment. Furthermore, eighteen selected genes with either moderate or high differential expression values from the microarray analysis were independently analyzed by quantitative real-time RT-PCR to confirm the reliability of the data. In our microarray analysis, the expressions of over 1310 genes were identified in response to Pb treatment. Extensive hierarchical clustering analysis of these responses indicated that the major consistently activated genes were also involved in common stress-induced responses. Especially, those that have been previously reported to be heavy metal inducible genes were significantly induced by lead treatment. Moreover, some important genes encoding enzymes or proteins involved in sulfur assimilation, GSH metabolism, indole-3-acedic acid (IAA) and jasmonic acid (JA) biosynthesis were activated, and these pathways were linked, directly or indirectly through signaling pathways, to biosynthesis of metal transports and detoxification molecules. Taken together, our results provided a new insight into the molecular mechanism of lead detoxification in Arabidopsis, and facilitated an understanding of the general lead/heavy metal-adaptive mechanism undertaken by plants.