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

137 Importance Of Seed Biotin Protein In Development Of Arabidopsis Thaliana Seeds
Libuse Brachova 1 , Hilal Ilarslan 2 , Eve Syrkin Wurtele 2 , Basil Nikolau 1
1
Iowa State University, Department of Biochemistry, Biophysics and Molecular Biology, Ames, IA, 2 Iowa State
University, Department of Genetics, Development, & Cell Biology, Ames, IA
Plants are a major source of biotin in the biosphere. The biochemical function of biotin as an enzyme cofactor is
to catalyze carboxylation, decarboxylation and transcarboxylation reactions. Furthermore, recent studies indicate that
biotin has a new function as a regulatory molecule, controlling gene transcription. Uniquely to plants, biotin appears to
be stored in seeds, covalently bound to a novel protein that hyper-accumulates in seeds. This Seed-Biotin Protein (SBP)
has been found in carrots, pea, soybean and Arabidopsis. To understand the physiological role of the SBP-bound biotin,
we have started to genetically characterize the function of this protein in Arabidopsis thaliana. We have identified two
independent mutant lines, in which the SBP-coding gene (At2g42560) is disrupted with T-DNA and SpM-transposon
insertions, respectively. Physiological, biochemical, and histological characterizations of these mutant lines indicate
that the biotin associated with the SPB protein is required for the timely establishment of the Arabidopsis seedling. The
phenotype associated with the loss of SBP function, can be reversed by the exogenous supply of biotin, indicating that
SBP does in fact act as a biotin-store that is required for timely establishment of seedlings.
138 Mutation of the MAP Kinase Gene MPK6 Reduces Male Fertility in Arabidopsis
Susan Bush, Suraphon Chaiwongsar, Patrick Krysan
Horticulture Department and Genome Center of Wisconsin, University of Wisconsin-Madison, Madison, WI
53706, USA
The Arabidopsis mitogen-activated protein kinase (MAPK) MPK6 is activated in response to a variety of stressors,
including low temperature, touch, wounding, salt, osmotic stress, pathogen attack, and ozone exposure. As part of a
comprehensive analysis of MAPK function in Arabidopsis, we are characterizing two independent T-DNA alleles of
MPK6. Our analysis has indicated that mutation of MPK6 causes low seed set that is likely to be due to defects in pollen
development and/or maturation. Analysis of mpk6 pollen by environmental scanning electron microscopy has revealed
mutant pollen to be less abundant and poorly dehisced from the anther compared to the wild-type. We are in the process of
completing a study of pollen development in mpk6 anthers based on the use of thin-section microscopy, which should allow
us to identify the stage of development at which mpk6 pollen become compromised, as well as the precise characteristics
of any developmental irregularities. Genevestigator, the Arabidopsis database of Affymetrix gene chip data, indicates
that the highest level of MPK6 expression occurs in the stamen and pollen, which is consistent with our observations of
reduced male fertility in mpk6 plants. We are currently characterizing the expression pattern of MPK6 using GUS- and
YFP-MPK6 fusion proteins in order to more precisely map MPK6 expression during floral development.