Mobility of micro-RNAs in Arabidopsis thaliana

MicroRNAs (miRNAs) are endogenous ~22nt RNAs with critical roles in plant development that silence endogenous mRNAs. Results from the Timmermans Lab have shown that miRNAs miR390 and miR166 can move intercellularly, acting outside their domain of biogenesis. These results propose a novel function for miRNAs as mobile signals in development. I investigated the parameters of miRNA mobility, such as tissue specificity, direction, and range. GUS reporter activity was analyzed in transgenic lines that ubiquitously express the cell autonomous GUS reporter as well as an artificial miRNA targeting GUS transcripts (miRGUS) from promoters with distinct expression profiles. GUS silencing in these lines was compared to expression domains of the specific promoters used. The chosen promoters are pATML1,pRbcs, and  pFIL, which are active in the leaf epidermis, the sub-epidermal layers, and the abaxial domain of the leaf respectively. These promoters will test miRNA mobility between different cell layers in young leaf primordia. Moreover, I tested pSUC2 pATHB8, and pSCR, which are active in vascular tissue and the cells surrounding the vasculature, respectively, and thus will test movement from the vasculature into adjacent cell types. The effects of miRNAs were partially proven to be dose dependent; a silencing effect was only seen when the promoter was exceptionally strong.  The results indicate that miRNAs can move from the leaf epidermis into the sub-epidermal layers. Further analysis is required to test additional parameters of miRNA mobility. Supported by NSF-URM Grant DBI-0731655.