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

139 WRINKLED1, an AP2/EREBP Class Transcription Factor, Plays a Vital Role in Seed Oil
Accumulation, Seed Germination and Seedling Establishment
Alex Cernac, Christoph Benning
MIchigan State University
The regulation and dynamics of seed oil accumulation and storage reserve utilization is a topic of economic and
scientific interest. Through density screening and visual scoring the wrinkled1 mutant of Arabidopsis was isolated. The
primary phenotype of wri1 is a defect in seed oil accumulation (80% TAG reduction wri1). Physiologically, the major
wrinkled1 defect in the developing embryo is in the activities of five glycolytic enzymes. Hexokinase and pyrophosphate
dependent phosphofructokinase activities were the most severely affected followed by pyruvate kinase and enolase
activities, with aldolase activity showing a minor reduction. Taken together the data support a global role for WRI1 in the
regulation of glycolysis. It was subsequently shown that WRI1 encodes an AP2/EREB domain protein and microarray
data have demonstrated the wri1 mutant results in a down regulation in the accumulation of transcript for a large number
of genes involved in carbon metabolism in the developing embryo. Examination of germination and gene expression
indicates that WRI1 plays a role in abscisic acid response in the germinating seed, possibly as a result of altered storage
reserve levels in the seed or altered metabolism which in turn affects abscisic acid response through sugar signaling. Our
recent elucidation of the DNA binding motif for WRI1 has allowed us to focus research efforts on the targets of WRI1
activity and further define the roles of WRI1 in the developing embryo and germinating seed.
140 A bHLH Protein Involved in Embryo Pattern Formation Interacts With DORNROESCHEN
(DRN) and DRN-LIKE and Reveals a Role for All Three Proteins in Seed Germination
John Chandler, Wolfgang Werr
Department of Developmental Biology, University of Cologne, Gyrhofstrasse 17, D-50923 Cologne, Germany
DRN and DRN-LIKE are two gene paralogues expressed from early embryo stages which redundantly control embryo
patterning. A gene encoding a basic helix-loop-helix (bHLH) protein was isolated from a yeast two hybrid screen using
the AP2 domain from DRN and DRN-LIKE as a bait. The protein-protein interactions were confirmed via both transient
bi-molecular fluourescence complementation in leek cells and by co-immunoprecipitation experiments. The expression
pattern of bHLH overlaps with DRN and DRN-LIKE in the early embryo and two independent mutant bhlh alleles
show more severe defects in embryo development than in drn and drn-like single mutants, showing that the bHLH gene
has an essential function in pattern formation. Double mutants between bhlh and drn and drn-like reveal an additional
novel delayed seed germination phenotype not seen in any of the single mutants, which can be partially overcome by
gibberellin. Taken together, our results show that this bHLH gene is a novel player in the complex network of regulatory
genes controlling embryonic pattern formation and implicates novel heterodimers involving at least two transcription
factor families in the control of seed germination.