Identification and analysis of seven H₂O₂-responsive miRNAs and 32 new miRNAs in the seedlings of rice (Oryza sativa L. ssp. indica).

Plant microRNAs (miRNAs) have been shown to play critical roles in regulating gene expression at the post-transcriptional level. In this study, we employed high throughput sequencing combined with computational analysis to survey miRNAomes from the seedlings of rice under normal conditions and treatments of H(2)O(2) that result in oxidative stress. Comparison of the miRNAomes and subsequent northern blot analysis identified seven miRNA families differentially expressed under H(2)O(2) stress. Predicted and experimentally validated targets of these H(2)O(2)-responsive miRNAs are involved in different cellular responses and metabolic processes including transcriptional regulation, nutrient transport, auxin homeostasis, cell proliferation and programmed cell death. This indicates that diverse miRNAs form a complex regulatory network to coordinate plants' responses under oxidative stress. In addition, we also discovered 32 new miRNAs in the seedlings of rice. Interestingly, of these new miRNAs, miR3981 was originally found to be a putative exonic miRNA located in the exon of AK106348, suggesting that plants may also use some exons as an miRNA source. This study is the first genome-wide investigation of H(2)O(2)-regulated miRNAs in plants and broadens our perspectives on the important regulatory roles of miRNAs in plant oxidative stress and physiological adaption.