Control of Plant Architecture: The Role of Phyllotaxy and Plastochron

Plants display a wide variety of three dimensional forms, or architectures, that are critical for their survival in competitive environments or, in the case of crops, for their productivity. Architecture is generated after embryogenesis through the activities of shoot apical meristems and root apical meristems. Leaves are the principal lateral organ that determines the plant shoot morphology, and they normally develop in very regular patterns in time and space. The spatial pattern of leaf arrangement is called phyllotaxy, and the temporal pattern is determined by the plastochron, which is the time between successive leaf initiation events. Both programs involve many gene activities as well as the hormones auxin and cytokinin. Apparently, the mechanisms controlling phyllotaxy and plastochron share some regulatory components. In this review, the molecular mechanisms for both patterning programs will be discussed.