PROCESSING OF miR319 AND miR172 MicroRNA PRECURSORS IN ARABIDOPSIS THALIANA

摘要

MicroRNAs (miRNAs) arc small RNAs of ～ 21 nt that recognize partially complementary sites in target mRNAs and guide them to cleavage or translational arrest. They are transcribed as larger precursors that contain fold-back structures that are processed by RNAse Ⅲ complexes. The precursor contains spatial clues that determine the position of the miRNA along its sequence. However, at a difference with animals, plant miRNA precursors are heterogeneous in size and shape, and the processing mechanisms still remain largely unknown. We have focused on miR172 and miR319 that regulate AP2 and TCP transcription factors respectively. Overexpression of miR172 precursor causes an early transition from vegetative to reproductive phase, while miR319 causes an increased cell proliferation and changes in leaf morphogenesis. Analysis of the processing intermediates of these miRNAs revealed that the miR319 precursor requires four sequential cuts to release the mature miRNA, instead of the two cuts observed in miR172. To analyze the structural requirements for miRNA processing, we have performed site directed mutagenesis on the precursors to change their spatial structure. We are currently analysing the processing intermediates of the different miRNA precursors in Arabidopsis plants.