RNA Sequencing−Mediated Transcriptome Analysis of a Naturally Occurring Uranium−Tolerant Species Prosopis juliflora

In the seasonal surveys carried out to identify the flora at the Tummalapalle uranium mine tailings of India, Honey Mesquite (Prosopis juliflora (SW.DC), a hardy plant, was identified as candidate species for phytoremediation of uranium contaminated soils. This plant species exhibit high uranium (U) tolerance and also accumulation. Although the U toxicity effects were studied on a few organisms, the physiological and molecular mechanisms of U detoxification in plants are poorly understood. Here, we analyzed a differential transcriptome of U-responsive genes in the roots using RNA-seq technology. A total of 1,42,290 transcript reads with an average length of 250bp were assembled into 85,088 unigenes by de novo assembly programme. Among them, 75,000 and 49,094 unigenes were annotated to NCBI BLASTX and Uniprot databases respectively. A total of 2,542 genes were down-regulated by U exposure, whereas 544 genes were up-regulated in the roots. The upregulated genes include: Zinc finger family proteins, aquaporins, TIP2-2-like, cation/H(+) antiporter 20-like, inorganic phosphate transporter-1-4-like, probable boron transporter 2-like and MATE efflux proteins, NAC11, WRKY41 etc. The ABC transporter family genes are the major family induced by U, indicating that U might be sequestered into the vacuole for detoxification. Most of the metabolic processes, genes were not significantly altered. A total of 15% uncharacterized unigenes was also observed in response to U stress, implicating their role in U tolerance and accumulation. Overall, our data provide a platform for further functional characterization of these genes involved in U tolerance and accumulation in plants.