75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

207 FAMA Controls The Switch Between Proliferation And Differentiation In Stomatal
Development.
Kyoko Ohashi-Ito, Dominique Bergmann
Department of Biological Sciences, Stanford University
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
(fama-1) has no morphologically identifiable stomata in any organ. Instead, fama-1 mutants make tumor-like clusters
in normal stomatal positions. We have shown that 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.
Overexpression of FAMA leads to a phenotype in epidermal cells that is the opposite of the loss of function phenotypes.
FAMA-OE 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. Further studies on the activity
of FAMA and its interaction with other stomatal regulators will be presented.
208 Analysis of ARF7- and ARF19- Regulated Genes in Arabidopsis Lateral Root Formation
Yoko Okushima 1 , Makoto Onoda 1 , Athanasios Theologis 2 , Masao Tasaka 1 , Hidehiro Fukaki 1
1
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Nara, Japan, 2 Plant Gene
Expression Center, UC Berkeley, Albany, CA
The members of Auxin Response Factor (ARF) regulate auxin-mediated gene expression during plant growth and
development. arf7 arf19 double mutants exhibit strong auxin-related phenotypes including severely impaired lateral root
formation, which not seen in each single mutant, suggesting that lateral root formation is redundantly regulated by ARF7
and ARF19 transcription factors. Global gene expression analysis has revealed that auxin-induced expression of many
genes, such as those encoding Lateral Organ Boundaries (LOB) domain (LBD)/AS2-like (ASL) proteins, are disrupted
in arf7 arf19 double mutants. Among these auxin-responsive LBD genes, LBD16 and LBD29 are specifically expressed
in root steles and young lateral root primodia, where ARF7 and ARF19 are also expressed. We found that overexpression
of LBD16 and LBD29 partially rescues the lateral root phenotype of arf7 arf19 double mutant, respectively. In addition,
target-gene analysis using the arf7 arf19 plants expressing ARF7-GR fusion protein indicates that ARF7 directly regulates
auxin-mediated gene expression of LBD16 and LBD29. These observations strongly suggest that at least ARF7 promotes
lateral root formation through the direct activation of auxin-responsive LBD16/29 expression. Furthermore, the transgenic
plants overexpressing LBD16 with transcriptional repression domain (SRDX) exhibit a strong auxin-related phenotype
including impaired lateral root formation. Together, our data strongly suggest that auxin-mediated induction of these
LBDs by ARF7/19 promotes lateral root formation in Arabidopsis.