Identification of cadmium-responsive microRNAs in Solanum torvum by high-throughput sequencing

MicroRNAs (miRNAs) play key roles in regulating Cd toxicity tolerance in plants. Solanum torvum Sw. is a typical low Cd-accumulating plant that has a high Cd tolerance. Despite its importance, no miRNA has been identified from S. torvum thus far. In this study, high-throughput sequencing of S. torvum small RNAs was used to identify miRNAs that were differentially expressed in response to Cd toxicity. At least 45 miRNA families and 165 individual members within those families were identified in both the control and Cd-treated S. torvum roots. Among these miRNAs, 45 miRNAs from 21 miRNA families were differentially expressed in the control and Cd-treated S. torvum plants. Among these 21 differentially expressed miRNA families, 6 miRNA families were upregulated in the Cd-treated roots, and 15 miRNA families were downregulated in Cd-treated roots. Bioinformatics analysis indicated that these miRNAs were involved in replication, recombination and repair, inorganic ion transport and metabolism, transcription, signal transduction mechanisms, cell cycle control, cell division, chromosome partitioning, RNA processing and modification in S. torvum roots. These results indicated that specific miRNAs are tightly regulated by Cd toxicity in the roots of S. torvum, which may play key roles in the Cd tolerance of S. torvum.