MicroRNA gene regulation cascades during early stages of plant development.

MicroRNAs (miRNAs) regulate various developmental programs of plants. This review focuses on miRNA involvement in early events of plant development, such as seed germination, seedling development and the juvenile to adult phase transition. miR159 and miR160 are involved in the regulation of seed germination through their effects on the sensitivity of seeds to ABA. miR156 and miR172 play critical roles in the emergence of vegetative leaves at post-germinative stages, which is important for the transition to autotrophic growth. The phase transition from the juvenile to adult stage in both monocots and dicots is also regulated by miR156 and miR172. In these early developmental processes, there are miRNA gene regulation cascades where the miR156 pathway acts upstream of the miR172 pathway. Moreover, targets of miR156 and miR172 exert positive feedback on the expression of MIR genes that suppress themselves. The early events of plant development appear to be controlled by complex mechanisms involving sequential expression of different miRNA pathways and feedback loops among miRNAs and their target genes.