Abstract
Selenium (Se) is an essential mineral element for animals and humans. Cardamine hupingshanensis (Brassicaceae), found in the Wuling mountain area of China, has been identified as a novel Se hyperaccumulator plant. However, the mechanism for selenium tolerance in Cardamine plants remains unknown. In this study, two cDNA libraries were constructed from seedlings of C. hupingshanensis treated with selenite. Approximately 100 million clean sequencing reads were de novo assembled into 48,989 unigenes, of which 39,579 and 33,510 were expressed in the roots and leaves, respectively. Biological pathways and candidate genes involved in selenium tolerance mechanisms were identified. Differential expression analysis identified 25 genes located in four pathways that were significantly responsive to selenite in C. hupingshanensis seedlings. The results of RNA sequencing (RNA-Seq) and quantitative real-time PCR (RT-qPCR) confirmed that storage function, oxidation, transamination and selenation play very important roles in the selenium tolerance in C. hupingshanensis. Furthermore, a different degradation pathway synthesizing malformed or deformed selenoproteins increased selenium tolerance at different selenite concentrations. This study provides novel insights into the mechanisms of selenium tolerance in a hyperaccumulator plant, and should serve as a rich gene resource for C. hupingshanensis.
Highlights
Selenium (Se) is an essential trace element for animals and humans that can be acquired from plant accumulators growing in seleniferous soil
When selenate and selenite are reduced to SeCys, there are three steps that will result in non-specific incorporation of Se into proteins: first, the selenocysteine lyase (SL) and NifS-like enzymes (CpNifS) break SeCys; second, SeCys methylation mediated by methyltrans- ferases (SMTs) is another important approach for seleniun detoxification and can increase the concentration of internal Se; third, cystathionine-γ-synthase (CγS) converts methylated SeCys to volatile DMSe16
The transcript abundance analyzed by bowtie and RNASeq by Expectation Maximization (RSEM) showed that 39,579 and 33,510 transcripts were expressed in the roots and leaves, respectively
Summary
Selenium (Se) is an essential trace element for animals and humans that can be acquired from plant accumulators growing in seleniferous soil. Yuan et al (2013) and Shao et al (2014) measured concentrations of total Se by hydride generation-atomic fluorescence spectrometry (HG-AFS) and HPLC-ICP-MS, respectively These studies showed that C. hupingshanensis could accumulate Se in excess of 1400 mg Se kg−1 of dry matter in all tissues of seedlings, with most not exceeding 4000 mg Se kg−1 of dry matter in roots[9,10]. When selenate and selenite are reduced to SeCys, there are three steps that will result in non-specific incorporation of Se into proteins: first, the selenocysteine lyase (SL) and NifS-like enzymes (CpNifS) break SeCys; second, SeCys methylation mediated by methyltrans- ferases (SMTs) is another important approach for seleniun detoxification and can increase the concentration of internal Se; third, cystathionine-γ-synthase (CγS) converts methylated SeCys to volatile DMSe16. Our study should be a useful reference for studying selenium tolerance in plants
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