Regulatory Role Analysis Of SiRNA And DNA Methylation In Rice(Oryza Sativa) Cadmium Accumulation

Endogenous small interfering RNAs (siRNAs) are a class of small non-coding RNAs that negatively regulate specific target mRNAs at the post-transcriptional level. DNA methylation is an epigenetic mark that silences gene at transcriptional level. Both siRNA and DNA methylation have been implicated in developmental processes and adaptations to environmental stresses. Cadmium (Cd) is a heavy metal toxic to humans and the accumulation of Cd in the rice grain is a major agricultural problem, particularly in Asia.Oryza sativa L. subsp. japonica cv. Xiushui11and Oryza sativa L. subsp. japonica cv. Xiushui110was used in this studies. Different Cd accumulation pattern in different stage of rice gowing was identified. Results indicated that Cd remove from xylem to leaves determined Cd content in phloem sap and fianaly Cd accumulation in rice grains. So, Cd absorption in rice leaves is a crucial process determined Cd accumulation in rice grams.To investigate the molecular mechanism of the response of Cd in rice, comparative Cd-responsive gene profiles between a high Cd-accumulating cultivar (Xiushui110) and a low Cd-accumulating cultivar (Xiushui11) were performed using real time PCR, in which the expression of OsPCR1in the leaves was significantly different between the two cultivars in life cycle under Cd stress.Furthermore, one siRNA from CRSD (siRNA database) was identified, and in the leaves of two cultivars, mRNA levels of the target gene of the siRNA, OsPCR1, were negatively correlated with the siRNA under Cd stress. The results provide evidence of the siRNA accumulation dysfunction of Xiushui110in response to Cd stress.Based on McrBC and real-time PCR assay, we determined the presence of differentially methylated fragments within the second exon region. This observation was consistent with the different OsPCR1expression level between the two cultivars. These findings suggested that epigenetic factors play an important role in the regulation of rice Cd-responsive gene expression, and highlighted a novel molecular mechanism of heavy metal response in plants.