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Transcription factor control of asymmetric cell divisions that establish the stomatal lineage


The establishment of new cell lineages during development often requires a symmetry-breaking event. An asymmetric division in the epidermis of plants initiates a lineage that ultimately produces stomatal guard cells. Stomata are pores in the epidermis that serve as the main conduits for gas exchange between plants and the atmosphere; they are critical for photosynthesis and exert a major influence on global carbon and water cycles1. Recent studies implicated intercellular signalling in preventing the inappropriate production of stomatal complexes2,3,4. Genes required to make stomata, however, remained elusive. Here we report the identification of a gene, SPEECHLESS (SPCH), encoding a basic helix–loop–helix (bHLH) transcription factor that is necessary and sufficient for the asymmetric divisions that establish the stomatal lineage in Arabidopsis thaliana. We demonstrate that SPCH and two paralogues are successively required for the initiation, proliferation and terminal differentiation of cells in the stomatal lineage. The stomatal bHLHs define a molecular pathway sufficient to create one of the key cell types in plants. Similar molecules and regulatory mechanisms are used during muscle and neural development5,6, highlighting a conserved use of closely related bHLHs for cell fate specification and differentiation.

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Figure 1: SPCH is required for asymmetric cell division and stomatal formation.
Figure 2: SPCH, a bHLH protein expressed in the epidermis and sufficient for asymmetric cell divisions and stomatal formation.
Figure 3: SPCH-related proteins also control stomatal development.

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We thank members of the lab for discussion and comment on the manuscript and K. Torii for discussions and communication of data before publication. Some stocks were obtained from the Arabidopsis Biological Resource Center (ABRC) at Ohio State University. These studies were supported by a US National Science Foundation grant. C.A.M. was supported by an NIH Training grant to Stanford University.

Sequences have been deposited in Genbank under accession numbers: DQ868373 (SPCH messenger RNA); DQ863645 (MUTE mRNA) and DQ864972 (MUTE genomic).

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Correspondence to Dominique C. Bergmann.

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The authors declare no competing financial interests.

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This file contains Supplementary Methods; Supplementary Figures and Legends 1-5; Supplementary Notes (PDF 1314 kb)

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MacAlister, C., Ohashi-Ito, K. & Bergmann, D. Transcription factor control of asymmetric cell divisions that establish the stomatal lineage. Nature 445, 537–540 (2007).

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