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

191 Regulation Of BDL Gene Expression In The Arabidopsis Embryo
Jasmin Ehrismann, Dolf Weijers, Marika Kientz, Gerd Juergens
Centre for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tuebingen, Auf der
Morgenstelle 3, D-72076 Tuebingen, Germany
Early embryogenesis in Arabidopsis is marked by a series of regulated divisions, that partition the embryo into
functionally distinct domains. During this process, different cell types are specified, but the mechanisms are largely
unknown. We have previously identified a pair of transcriptional regulators, the activator MP and its inhibitor BDL, that
are critical for initation of the embryonic root. Importantly, differential expression of MP and BDL genes is associated
with several cell-specification events, including the establishment of apical and basal lineages after the first zygotic
division. Hence, identification of cis-elements and transcription factors that regulate MP or BDL expression will
shed light on the mechanisms that act in early embryo patterning. We focused our attention on the BDL gene and first
generated transcriptional and translational reporter fusions to visualize gene and protein expression, and next preformed
performed deletion experiments to narrow down the cis-elements for BDL gene expression to a 50 bp element in the
proximal promoter region.. We are currently using yeast 1-hybrid screens to identify transcription factors that bind to
this element. We will present the systematic cis-element deletion analysis of the BDL gene and the identification and
functional analysis of candidate regulators.
192 Brassinosteroids Regulate Plant Architecture by Controlling Organ Boundaries in Shoot
Tissues
Joshua Gendron 1, 2 , Dongmei Cao 3 , Nathan Gendron 1 , Kang Chong 3 , Zhi-Yong Wang 1
1
Carnegie Institution of Washington at Stanford, Stanford, CA, 2 Stanford University, Stanford, CA, 3 Chinese
Academy of Sciences, Beijing, China
Brassinoteroids (BRs) are essential plant hormones that are required for proper development and growth. Much is
known about how BRs are made, perceived, and transduced as a signal, and it is well established that BRs play a major
role in cell expansion. Little is known about whether or how BRs affect development outside of this role in cell expansion.
In this work we show that BRs are involved in establishment of organ boundaries. Organ fusion phenotypes were first
noticed in the bzr1-1D mutant, which contains a gain of function mutation in a transcription factor that acts as a positive
regulator of BR signaling. bzr1-1D shows kinking of the main stem towards the lateral branches, and BR deficient and
insensitive mutants show kinking of the stem away from the lateral branches. Cross sections of the stem-branch junction
in bzr1-1D reveal a change in the boundary between the axil cells and the elongating cells of the stem. Additionally,
scanning electron microscopy revealed an abnormal fusion of the cauline leaf to the stem. Furthermore, fusions are
observed in the bzr1-1D mutant between floral organs within and between whorls. Specifically, bzr1-1D contains stamenstamen
and stamen-carpel fusions, the latter resulting in bent siliques. Brassinolide (BL) treatment of wildtype plants, or
induction of an inducible DWF4 biosynthetic gene, leads to stamen-stamen fusion. Additionally, decreased BR signaling
leads to abnormal organization of floral organs. A screen for suppressors of the bzr1-1D fusion phenotypes has lead to
the identification of intragenic and extragenic suppressors that show no organ fusion phenotypes. GFP tagged versions
of the BZR1 wildtype and mutant proteins accumulate in the nuclei of cells in the floral organs demonstrating that BZR1
protein is expressed in the organs that show these fusion defects. Additionally the BZR1 mutant protein accumulates
highly in the inflorescence and floral meristems suggesting that it is indeed functioning early in development of the floral
organs. Currently we are investigating the effects of BRs on expression of various genes involved in meristem function,
including CUC-GFP, CyclinB-GUS, STM-GUS, and others. These results demonstrate that BRs not only determine plant
size through regulation of cell expansion but are also involved in developmental patterning and organ separation.