Functional Analysis On Cadmium Response Of MiR192、miR166and It’s Target HD-Zip In Rice (Oryza Sativa)

MicroRNAs (miRNAs) are a class of endogenous small non-codingRNAs with the length of21-27nucleotides in eukaryote organisms. PlantmiRNAs, as negative regulators of gene expression at the post-transcriptionallevel, have important roles in developmental processes and stress response.The target genes of miRNAs are usually the transcription factors involved inplant development and signal transduction pathways, implying that miRNAsare essential components in gene regulatory network.A Japonica rice Zhonghua11was used in the studies. miR192andmiR166were identified to be Cd-responsive miRNAs based on miRNAmicroarray. Transgenic over-expression miR192and over-expression miR166lines were obtained to investigate their roles in Cd tolerance. Over-expressionof miR166made the roots and seedlings grow stronger under Cd stress thanwild type controls, indicating that over-expression of miR166increased Cdstress tolerance, but over-exprssion miR192increased Cd stress sensitivity.Target genes were predicted for the miR166and miR192, which encodedtranscription factors Homeodomain leucine zipper protein（HD-Zip） andATP binding protein （ABC）, they were reported to be associated withmetabolic processes such as growth, signal transduction, and stress responses.Furthermore, the HD-Zip mRNA levels were negatively correlated withmiR166under Cd stress. Then we constructed the over-expression andRNAi-expression vectors of HD-Zip and transformed them into wild typeZhonghua11. These results will help to understand the plant heavy metalstress response mechanisms, and provide an effective approach to improvestress tolerance of plants.