21 Feb 2014
Dominique Bergmann
Department of Biology
Stanford University
During development, all multicellular organisms face a similar set of challenges: they must create a diverse set of specialized cell types and organize these cells into functional tissues and organs. Each organism has a stereotyped size and morphology, yet only the simplest of bodyplans can arise from an invariant set of development steps – more often there is variation along the developmental path, even when the endpoint is the same. For plants, in which the environment plays a considerable role in their development, pattern formation, coordinated growth and environmental homeostasis are inextricably linked. This stands in contrast to animals where temporally distinct phases (1) lay down pattern (embryogenesis, from which animals emerge with a body plan essentially the same as an adult) and (2) engage in growth and homeostatic responses (postembryonic to adult life). Fortunately, for all the complexity the integrated habit creates, there are also some simplifying features of plant development. For example, cells do not migrate or undergo cell death, so morphogenesis and pattern arise solely from patterns of cell division and differential expansion. Over the last decade, genetic programs for leaf development have been largely worked out, and these resemble animal programs in their reliance on cell-type specific transcription factors and extensive cell-cell signaling. Recently, we have been taking more integrative approaches to understanding how stem-cell like lineages in the leaf epidermis are regulated in concert with external influences. As each newly formed leaf is a "developmental blank slate", by tracking divisions and gene activities from its initiation to maturity, we generated simple models to explain pattern through a postmitotic polarity-switching mechanism [1]. Our current challenge is to refine these models to take into account developmental histories and environmental factors, and to address the long-debated questions about whether the epidermis drives organ growth, or whether (and how) whole organ pattern and size control emerges from decentralized control.