Abstract
Growth and development in plants is organized as a series of developmental stages, most importantly embryogenesis, vegetative, and reproductive growth. The timing of transitions between those stages is highly regulated to allow the successful completion of a life cycle by producing maximum numbers of progeny. Targets of both miR156 and miR172 have been implicated in the timely control of several phase transitions in various plant species. This chapter describes the role of both miRNAs’ targets as well as the regulatory information provided by miRNA-mediated repression of their accumulation.