Age-dependent heteroblastic development of leaf hairs in Arabidopsis.

Higher plants progress through a juvenile and an adult phase of development before they enter the reproductive phase. The transition from the juvenile to the adult phase is referred to as vegetative phase change, and this is signified by the production of trichomes on the abaxial side of leaf blades in Arabidopsis; however, the molecular mechanism underlying this process is poorly understood. We identified a dominant mutation (gl1-D) in a forward genetic screen that accelerates abaxial trichome production during shoot development. This phenotype is the result of a G-to-A substitution in the 3' noncoding region in the GLABRA1(GL1) gene. We show that TOE1, an AP2-like transcription factor that acts downstream of the miR156-SPL pathway, represses GL1 expression by directly binding to this site, and that gl1-D prevents TOE1 binding. Our work reveals a molecular link between vegetative phase change and abaxial trichome production in Arabidopsis, and answers a long-standing question of how the vegetative phase change pathway regulates vegetative traits.