15th International Conference on Arabidopsis Research - TAIR

T01-019
A SUMO specific protease that regulates flowering of
Arabidopsis
Yong-Fu Fu(1), Paul H. Reeves(1), Giovanni Murtas(1), George Coupland(1)
1-Max-Planck-Institut für Züchtungsforschung, 50829 Köln, Germany
Post-translational modification is important in regulation of protein function.
The covalent attachment of the ubiquitin-like modifier (SUMO) to its targets
(sumoylation) represents, after ubiquitylation, the best-studied example
of a protein modification by attachment of a peptide to target proteins.
Accumulating evidence shows that sumoylation is involved in a wide range
of biological processes, including transcription, the cell cycle, apoptosis,
chromatin integrity and dynamics, and nucleocytoplasmic transport. Protein
sumoylation may regulate plant development since the Arabidopsis genome
contains genes predicted to encode all the components of the SUMO system
defined in other organisms. The early in short days 4 (esd4) mutant showed
extremely early flowering in both long days and short days and alterations
in other developmental events. We have identified ESD4 and shown that
it encodes a protease with strong similarity to yeast and animal proteases
specific to SUMO. ESD4 has the activity in vitro of a SUMO protease, and
is responsible in vivo for recycling SUMO from SUMO-conjugates, because
esd4 mutants accumulated higher levels of SUMO-conjugates compared to
wild type plants and over-expression of SUMO enhanced the biochemical and
morphological phenotype of esd4. ESD4 is localized at the periphery of the
nucleus. We are identifying SUMO targets with affinity purification following
by 2-DE and MALDI-TOF and try to explain how the SUMO system is involved
in flowering control.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-020
Genetic evidence for essential calcium transporters
in pollen growth and fertilization.
Frietsch, S.(1), Romanowsky, S.M.(1, 2), Schiøtt, M.(3), Palmgren, M.G.(3), Harper,
J.F.(1, 2)
1-The Scripps Research Institute, Department of Cell Biology, La Jolla, California 92037, USA
2-University of Nevada, Department of Biochemistry, Reno, Nevada 89557
3-The Royal Veterinary and Agricultural University, Department of Plant Biology, DK-1871 Frederiksberg,
Denmark
Calcium dynamics are thought to play a central role in pollen development,
as evidenced by pharmaco-chemical approaches and visualization of calcium
gradients and oscillations. Using Arabidopsis as a model system, we provide
the first genetic evidence to support a model in which calcium signals are
natural regulators of pollen tube growth and fertilization. Calcium signals are
largely controlled by influx (through channels) and efflux (through pumps and
antiporters). We have identified T-DNA gene disruptions in all 14 calcium
pumps, and 18 of 20 cyclic nucleotide gated channels (CNGCs). From this
set of mutants, distinct pollen specific phenotypes have been found for disruptions
of ACA9 (a calmodulin activated plasma membrane calcium pump)
and CNGC18 (a cyclic nucleotide and calmodulin regulated putative calcium
channel).
Calcium Pump Mutation: Three independent gene disruptions in ACA9
resulted in partial male sterility. Homozygous aca9 mutants showed an 80%
reduction in seed set. Mutant aca9 pollen displayed a reduced growth potential
and a high frequency of aborted fertilization.
Channel Mutation: Two independent disruptions in CNGC18 resulted in
complete sterility. We were unable to identify a homozygous mutant in more
than 400 F1 progeny. In vitro germination of heterozygous cngc18 pollen
in the quartet background showed that mutant pollen tubes germinate, but
only grow a short distance, with a “kinky-like” non-directional growth, often
prematurely terminating with a bursting event.
Although the aca9 and cncg18 mutants show defects in different stages of
pollen tube development, they both identify pollen specific ion transporters
that are regulated by calmodulin. A hypothesis to be tested is that both ACA9
and CNGC18 are essential for calmodulin-regulated calcium oscillations required
for plasma membrane signaling during pollen growth and fertilization.
Schiøtt et al., (2004) A plant plasma membrane Ca2+ pump is required for pollen tube
growth+fertilization. PNAS in press
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin