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

161 Global and Locus-Specific Roles for Arabidopsis Paf1C Homologs in Transcription and
Chromatin Modifications
Sookyung Oh, Steven van Nocker
Program in Plant Breeding and Genetics, Michigan State University, East Lansing, Michigan 48824
RNA Polymerase II-Associated Factor 1 Complex (Paf1C) in budding yeast plays a key role in reinforcing
transcriptional activity by mediating the establishment and/or maintenance of specific chromatin modifications, promoting
elongation and linking Pol II with elements of pre-mRNA processing machinery. This transcription factor is associated
with chromatin at all canonical transcriptional units yet investigated and therefore probably plays a general transcriptional
role.
Although components of Paf1C are conserved in higher eukaryotes, their potential mechanism in transcription has
not been explored. In Arabidopsis, Paf1C subunit homologs are encoded by the VERNALIZATION INDEPENDENCE
(VIP) genes. We found that loss of VIP gene function affects a substantial portion of the transcriptome, but strongly
silences only a small subset of genes including the FLC/MAF family of MADS-domain flowering regulators.
To better understand the mechanism of VIP proteins in transcription, we characterized genome-wide and locusspecific
effects of loss of VIP proteins on histone modifications and Pol II distribution. We analyzed methylation and
acetylation sites (Lys-4, Lys-9, Lys-14, Lys-36) on the major canonical and variant histone H3 proteins, and found that at
least VIP3 does not play a significant role in establishing these modifications when evaluated on a whole-chromatin level.
However, we found that VIP proteins are required for specific chromatin modifications within a subset of VIP-dependent
genes. Loss of VIP3 resulted in a decrease of Pol II density throughout FLC chromatin, including the promoter regions,
suggesting the major influence on FLC expression is through Pol II recruitment and transcriptional initiation rather than
elongation or pre-mRNA processing.
162 Female sporophytic Arabidopsis mutants impaired in pollen tube guidance
Yiding Huang, Ravi Palanivelu
Univeristy of Arizona, Univeristy of Arizona
A pollen tube's journey to an egg cell within the pistil involves cell to cell interactions such as attraction, repulsion
and adhesion. This journey begins with pollen tube growing between the walls of the stigma cells, travelling through
the extracellular matrix of the transmitting tissue, and finally arriving at the ovary, where it migrates up the funiculus,
and enter the micropyle of an ovule to deliver the two sperm cells, one fertilizes an egg and other the central cell. Thus a
pollen tube navigates past several different female cells before it reaches the egg and seeds are not produced if the pollen
tube guidance process is disrupted. To isolate pollen tube guidance signals from female sporophytic cells, we performed
a mutant screen by visually selecting Arabidopsis plants with reduced seed containing siliques from among the SALK
TDNA insertion collection. Mutations that cause reduction in seeds for other reasons besides pollen tube growth and
guidance defects male sporophytic and gametophytic defects (reduced or lack of pollen), pollination defects (reduced or
lack of pollen on the stigma), embryo and endosperm lethality (shriveled seeds) and fully penetrant female gametophytic
defects (~ half the number of seeds) were eliminated from the screen. To date, a primary screen of 5000 lines resulted
in twenty candidate mutants. These candidate lines were then subjected to a series of assays to select only those lines
that are impaired in pollen tube guidance. Based on the progeny analyses and reciprocal crosses to wild type plants we
confirmed that at least two of these lines are impaired in pollen tube guidance due to female sporophytic tissue specific
mutations. Progress on microscopy and in vitro pollen tube guidance analyses of mutants, and cloning the genes that are
tagged with TDNA will be reported.