Abstract
Stomata are essential for the exchange of gases and water vapor between a plant and its environment. Although previous studies revealed several factors involved in the signaling that creates normal stomatal pattern, less is known about the positive regulators of stomatal differentiation. We are studying FAMA, a bHLH transcription factor, which is highly expressed in plants having excess stomata and repressed in plants without stomata. A T-DNA insertion line of FAMA has no morphologically identifiable stomata in any organ. Instead, fama mutants make tumor-like clusters in normal stomatal positions. The cells in these tumors express markers of developing stomata, but do not express mature stomatal markers. FAMA RNA and protein are expressed in specific cells of the stomatal lineage. FAMA-overexpressing plants make many ectopic unpaired-guard cells. These results suggest that FAMA's function is to promote differentiation of guard cells and to inhibit excess cell divisions in stomatal development.
