Abstract
The Sedum alfredii Hance hyperaccumulating ecotype (HE) has the ability to hyperaccumulate cadmium (Cd), as well as zinc (Zn) and lead (Pb) in above-ground tissues. Although many physiological studies have been conducted with these plants, the molecular mechanisms underlying their hyper-tolerance to heavy metals are largely unknown. Here we report on the generation of 9.4 gigabases of adaptor-trimmed raw sequences and the assembly of 57,162 transcript contigs in S. alfredii Hance (HE) shoots by the combination of Roche 454 and Illumina/Solexa deep sequencing technologies. We also have functionally annotated the transcriptome and analyzed the transcriptome changes upon Cd hyperaccumulation in S. alfredii Hance (HE) shoots. There are 110 contigs and 123 contigs that were up-regulated (Fold Change ≧2.0) and down-regulated (Fold Change ≦0.5) by chronic Cd treatment in S. alfredii Hance (HE) at q-value cutoff of 0.005, respectively. Quantitative RT-PCR was employed to compare gene expression patterns between S. alfredii Hance (HE) and non-hyperaccumulating ecotype (NHE). Our results demonstrated that several genes involved in cell wall modification, metal translocation and remobilization were more induced or constitutively expressed at higher levels in HE shoots than that in NHE shoots in response to Cd exposure. Together, our study provides large-scale expressed sequence information and genome-wide transcriptome profiling of Cd responses in S. alfredii Hance (HE) shoots.
Highlights
The non-essential heavy metal cadmium (Cd) in soils is very mobile and readily enters plant tissues, the food chain and drinking water
The Crassulaceae family plant S. alfredii Hance (HE) is the only identified Zn and Cd hyperaccumulating plant to date that does not belong to Brassicaceae family [6].The major strategy hyperaccumulators have used is to protect themselves by compartmentalization of metal ions in the cell
Several contigs related to cell wall deposition and modifications were identified as Cd responsive genes in S. alfredii Hance (HE) shoots in the current study
Summary
The non-essential heavy metal cadmium (Cd) in soils is very mobile and readily enters plant tissues, the food chain and drinking water. Cd is toxic to plant tissues, adversely affecting the photosynthetic apparatus, carbohydrate metabolism and nitrate absorption [3]. Tolerant plants differ in the ways in which they contend with Cd. ‘‘Excluders’’ tolerate heavy metals by limiting the entry and root-to-shoot translocation of trace metals. Hyper-accumulating plants can accumulate extremely high levels of heavy metals in their above-ground tissues without exhibiting toxicity symptoms. Hyper-accumulating plants show promise for use in phytomediation, i.e., for cleaning up heavy metal contaminated sites and reducing the bioavailability of heavy metals in the environment [4]. The use of hyperaccumulators for this purpose has been limited due to their low biomass, lack of metal selectivity or poor agronomic practice
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