Figure 7.

Proposed Model for Transcription Factor Control of Stomatal Guard Cell Differentiation.

Genes that promote guard cell identify and structure must be upregulated while cell division promoting processes are coordinately downregulated. The transcription factors FAMA, FLP, and MYB88 are all required for the production of the normal two-celled stoma, but the processes they regulate may be different. FLP/MYB88 may work primarily to stop excessive cell divisions. FAMA may activate differentiation genes and either secondarily feedback on the cell cycle or require a partner to directly influence cell cycle gene transcription.