Book of Abstracts - Geyseco

02 - PS - Parallell Sessions Lectures
The nine-member β-amylase (BAM) gene family in Arabidopsis
is a good example of this. β-Amylase is known as a key enzyme
involved in starch degradation. In Arabidopsis, starch is accumulated
as a primary product of photosynthesis in leaves during the
day, serving as a transitory store of carbohydrate for use during
the night. β-Amylases liberate maltose molecules from the ends
of the glucan chains that comprise starch. Mutations in Arabidopsis
that cause a deficiency in chloroplastic β-amylase (BAM1 and
BAM3) result in a block in starch breakdown and an accumulation
of leaf starch. However, the chloroplast contains another
type of β-amylase-like protein which appears to be non-catalytic
(e.g. BAM4). Mutational studies show that these proteins are
also important in starch breakdown, although the mechanism by
which they act is as-yet unclear. Surprisingly, two Arabidopsis
β-amylase-like proteins, BAM7 and BAM8, are nuclear localised
and share an amino-terminal DNA-binding domain with a family
of plant-specific transcriptional regulators involved in plant
steroid hormone signalling. Deregulation of BAM7 and BAM8
expression results in altered plant growth and development, to
altered brassinosteroid sensitivity, but not to altered starch metabolism.
We have identified the DNA motif to which these two
proteins bind and obtained in-vivo evidence that they are transcriptional
activators. Homologous genes have been identified in
other plants including gymnosperms, and angiosperms (both monocot
and dicot species), implying that their functional specialisation
occurred early in higher plant evolution. Our hypothesis is
that the duplication of the genes encoding β-amylases has given
rise to metabolic sensors that control metabolism and provide a
regulatory link between carbon availability and growth control.
PS14: PLANTS &
GLOBAL CHANGE
Session lead lectures
PS14-001 GLOBAL CHANGE AND THE EFFECTS OF SO-
LAR UV RADIATION ON TERRESTRIAL ECOSYSTEMS
Ballaré, C.*
Universidad de Buenos Aires and CONICET
*Corresponding author, e-mail: ballare@ifeva.edu.ar
UV radiation (280-400 nm) is a minor component of the solar
spectrum reaching the ground surface; yet, it has important
effects on organisms and biogeochemical cycles. Many research
efforts during the past two decades have thoroughly characterized
the effects of the UV-B (280-315 nm) component. In this
talk, I will summarize the lessons from this previous work, and
highlight some of the important knowledge gaps in connection
with the effects of climate change. I will address the following
points. A) The effects of UV-B radiation on the growth (biomass
accumulation) of terrestrial plants are relatively small. B) On the
other hand, UV radiation affects plant secondary chemistry and
the activities of canopy arthropods and phyllosphere microorganisms.
Therefore, trophic interactions in terrestrial ecosystems
are likely to be significantly affected by future variations in UV
irradiance. C) Changes in UV resulting from climate change
(e.g., variations in cloud cover) may have more important consequences
on terrestrial ecosystems than those derived from ozone
depletion. This is because the resulting variations in UV may
affect a greater range of ecosystems, and will not be restricted
solely to the UV-B component. D) Several processes that are not
particularly sensitive to UV-B can be strongly affected by UV-A
radiation (315-400 nm). One example is the physical degradation
of plant litter. Recent work suggests that increased photodegradation
(in response to reduced cloudiness or reduced canopy cover)
may have important direct and indirect effects on carbon sequestration
in terrestrial ecosystems.
PS14-002 BEYOND 2050: CAN WE EXPECT CO2 SATU-
RATION OF LEAVES AND ECOSYSTEMS?
Ellsworth, D.*
University of Western Sydney
*Corresponding author, e-mail: D.Ellsworth@uws.edu.au
As atmospheric CO 2
concentration is rising, one important suite
of responses of ecosystems to the atmosphere are those involving
the carbon cycle, mediated by photosynthesis. However,
leaf photosynthesis saturates at [CO 2
] air
of 500-700 ppm, and
hence further increases in [CO 2
] may suggest no additional impact
on ecosystem C cycles beyond these concentrations. Others
have suggested that ecosystems are already saturated at current
atmospheric [CO 2
] levels, in part due to nutrient limitations and
severe water stress. Here, I will consider the question: are further
increases in ecosystem CO 2
flux or productivity in native
ecosystems possible beyond the photosynthetic CO 2
saturation
threshold? And which systems are closest to this threshold? Results
from a series of elevated CO 2
experiments, ecosystem CO 2
flux measurements, and from natural phenomena such as the European
drought of 2003 are used to provide evidence of plant and
ecosystem CO 2
saturation. Whilst the short-term mechanism of
photosynthetic response would suggest a large CO 2
stimulation
effect under drought, the longer-term response is very different.
The findings have relevance to the Mediterranean region as well
as to the significant fraction of global ecosystems that are nutrient-
and water-limited.
PS17: PLANT-MICROBE INTE-
RACTIONS
Session lead lectures
PS17-001 THE TOMATO – FUSARIUM OXYSPORUM PA-
THOSYSTEM
Rep, M.* - Houterman, P. - Gawehns, F. - Ma, L. - de Sain, M. -
Lukasik, E. - van der Does, C. - Cornelissen, B. - Takken, F.
University of Amsterdam
*Corresponding author, e-mail: M.Rep@uva.nl
The tomato xylem-colonizing fungus Fusarium oxysporum f.sp.
lycopersici (Fol) secretes small proteins into xylem sap of its
host. Three of these ‘effectors’ trigger effector-mediated immunity:
Avr1, Avr2 and Avr3 (or their activities) are recognized by the
resistance proteins I, I-2 and I-3, respectively. Interestingly, Avr1
suppresses I-2 and I-3-mediated resistance. Several Fol effectors
were shown through gene knock-out to contribute to virulence
towards susceptible plants. The genes for the effectors in Fol that
we identified reside on a ‘pathogenicity chromosome’. This chromosome
can be transferred between genetically isolated strains
of the asexual fungus, conferring host-specific pathogenicity to
the recipient.
We aim to uncover the molecular mechanisms by which effectors
of Fol trigger susceptibility (suppression of resistance) and
immunity (activation of R proteins), beginning with localization
of effectors in plant cells and identification of host proteins with
which they interact.
PS17-002 PLANT TARGETS OF BACTERIAL TYPE III
EFFECTOR PROTEINS
Bonas, U.*
Department of Plant Genetics, Martin-Luther-University Halle-
Wittenberg, Halle (Saale), Germany
*Corresponding author, e-mail: bonas@genetik.uni-halle.de
We study the interaction between pepper and tomato and the
Gram-negative plant pathogenic bacterium Xanthomonas campestris
pv. vesicatoria (Xcv), which causes bacterial spot disease
on its host plants. Successful interactions of Xcv with the plant
depend on a functional type III secretion (T3S) system, a molecular
syringe, which injects more than 20 effector proteins (termed
Avr or Xop = Xanthomonas outer protein) into the plant cell cytoplasm.
Among the Xops we find suppressors of the plant innate
immunity, putative enzymes and transcription factors. One of the
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