Seminars

Specification and maintenance of cell identity are central processes of development. In an effort to understand the regulatory networks that control cell identity, we have profiled all cell types and developmental stages within a single organ, the Arabidopsis root. To acquire global expression profiles we developed technology that uses sorted marked populations of cells with subsequent hybridization of the labeled RNA to microarrays. We are using computational methods to infer networks functioning within different cell types and developmental stages and have begun to test the hypothesized relationships.

Another key process in the development of multicellular organisms is precise regulation of asymmetric cell division to generate diverse cell types. The molecular mechanisms responsible for this process are still poorly understood, in particular how developmental pathways trigger asymmetric divisions. Asymmetric divisions in the Arabidopsis root are controlled by a finely orchestrated interplay between the transcription factors SHORTROOT (SHR) and SCARECROW (SCR). Our studies provide evidence for a direct mechanistic link between development and cell cycle progression as well as between organ patterning mechanisms and asymmetric cell division. In plant roots the radial tissue organization is highly conserved with a central vascular cylinder in which two water conducting cell types, protoxylem and metaxylem, are patterned centripetally. We have evidence that this patterning occurs through crosstalk between the vascular cylinder and the surrounding endodermis mediated by cell-to-cell movement of a transcription factor in one direction and a microRNA in the other.

This work is supported by grants from the NIH, NSF and DARPA.