Abstract
MicroRNAs (miRNAs) are endogenous non-coding small RNAs that play vital regulatory roles in plant growth, development, and environmental stress responses. Cadmium (Cd) is a non-essential heavy metal that is highly toxic to living organisms. To date, a number of conserved and non-conserved miRNAs have been identified to be involved in response to Cd stress in some plant species. However, the miRNA-mediated gene regulatory networks responsive to Cd stress in radish (Raphanus sativus L.) remain largely unexplored. To dissect Cd-responsive miRNAs and their targets systematically at the global level, two small RNA libraries were constructed from Cd-treated and Cd-free roots of radish seedlings. Using Solexa sequencing technology, 93 conserved and 16 non-conserved miRNAs (representing 26 miRNA families) and 28 novel miRNAs (representing 22 miRNA families) were identified. In all, 15 known and eight novel miRNA families were significantly differently regulated under Cd stress. The expression patterns of a set of Cd-responsive miRNAs were validated by quantitative real-time PCR. Based on the radish mRNA transcriptome, 18 and 71 targets for novel and known miRNA families, respectively, were identified by the degradome sequencing approach. Furthermore, a few target transcripts including phytochelatin synthase 1 (PCS1), iron transporter protein, and ABC transporter protein were involved in plant response to Cd stress. This study represents the first transcriptome-based analysis of miRNAs and their targets responsive to Cd stress in radish roots. These findings could provide valuable information for functional characterization of miRNAs and their targets in regulatory networks responsive to Cd stress in radish.
Highlights
Cadmium (Cd) is a widespread heavy metal pollutant that is highly toxic to living organisms
To investigate the roles of miRNAs thoroughly in regulatory networks responsive to Cd stress in radish, two sRNA libraries were constructed from Cd-free and Cd-treated radish roots and sequenced by the Solexa/Illumina system
In order to obtain global mRNAs from radish, an mRNA library constructed from total RNAs of radish root was sequenced by the Illumina/Solexa system, resulting in the generation of ~71.95 million raw reads
Summary
Cadmium (Cd) is a widespread heavy metal pollutant that is highly toxic to living organisms. Vast areas of agricultural soils are contaminated with Cd via atmospheric deposition and direct application of phosphate fertilizers, animal manure, sewage sludge, and irrigation water (Uraguchi et al, 2009; Wiebe et al, 2010). Due to its high mobility and water solubility, Cd2+ is readily taken up by plant roots and can be translocated into aerial organs. Cd2+ inhibits plant growth and development mainly through alterations in photosynthesis, respiration, and nitrogen metabolism, as well as a decrease in water and basic mineral nutrient uptake (BessonBard et al, 2009). Cd can accumulate in the human body over time via the food chain, resulting in a risk of chronic toxicity to kidney tubules , bone, lungs and some other organs.
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