Proteomic Analysis of Arabidopsis
thaliana in Microgravity
The function and
appearance of cells (and the organism that
the cells compose) are determined by the
specific proteins the cells produce. The
overall goal of this project is to
determine which proteins plants produce,
degrade, and modify in response to growth
in space. To do this, we're going to send
some Arabidopsis seedlings to grow on the
international space station, while
identical control plants are kept on earth
for comparison. We'll then use
Proteomics to compare the total protein
content of each set of plants.
There are
several potential benefits from this
research. Extended, manned space
exploration will require plant growth for
both food and oxygen. Understanding how
plants handle the stresses of space, not
only on a physioilogical level, but also a
molecular one, will be critical. In
addition, this analysis will reveal
candidate genes that we can use to better
understand how plants respond to the
constant force of gravity here on earth.
This has potential to inform agricultural
practices, as well as provide specific
targets for genetic engineering.
To gain a unique
perspective on the well-studied process of
gravitropism, we focus on the Gravity Persistent
Signal (GPS) response as a means to dissect cell
signaling in Arabidopsis (Fukaki et al.,
1996). At cold temperatures (4°C),
Arabidopsis inflorescence stems do not respond
to gravity due to an inhibition of auxin
transport (Nadella et al., 2006). However,
when a plant is subjected to a 90°
gravistimulation at 4°C, and subsequently
returned to room temperature in a vertical
orientation, the inflorescence stem displays a
transient bending in the direction that would
have been “up” when it was oriented horizontally
in the cold. The bottom line is that a
plant ends up bending to the side at room
temperature after a gravistimulation in the
cold. This is referred to as the Gravity
Persistent Signal (GPS) response. It is
thought to be caused by a buildup of signaling
proteins and secondary messengers during the
cold treatment that have no outlet without the
ability to transport auxin. Previous work
suggests that the GPS process is ideal for
analyzing the gravitropic pathway in a
simplified system, allowing for the discovery of
signaling components that may otherwise have
undetectable mutant phenotypes due to redundant
function (Wyatt et al., 2002).
Currently,
the lab is focused on two gravity persistent signal (gps) mutants in
Arabidopsis that display an aberrant response
to gravity after a cold treatment. One
of these, gps4, displays no
gravitropism after a GPS treatment.
Although its molecular identity is known, the
exact function of GPS4 remains a
mystery. The gps5 mutant displays
enhanced gravitropism in the root, hypocotyl
and inflorescence stem after a 90° gravitropic
stimulus. Furthermore, gps5 has drastically
increased root and hypocotyl growth.
Currently, research is focused on identifying
the molecular target of GPS5, and determining
its role in plant growth and development. This
project has been supported by the Summer
Research Fellowship and the Undergraduate
Research and Creative Activities awards at
SIUE.
Chlorophyll Synthesis
The synthesis of
chlorophyll is a critical, highly regulated
process in plants. To gain information
about this process, we are working with an
Arabidopsis line that has a mutation in the GERANYL
GERANYL DIPHOSPHATE SYNTHASE gene, ggps1-1,
that produces a variegated phenotype. It
is not currently understood why this plant can
produce chlorophyll at the leaf periphery, but
not in the center. We do know that the
phenotype is temperature sensitive. When
grown at warm temperatures, the albino sectors
grow, while growth at cooler temperatures lead
to completely green leaves. We are
currently trying to understand the link between
temperature and variegation.
ggps1-1
Time
course of ggps1-1 growth in cool and warm
conditions. Figure by Kelsey Kropp.
Publications
Ruppel,NJ,
Kropp, KN, Davis, PA, Martin, AE, Luesse, DR, and
Hangarter, RP. (2013)Mutations
in GERANYLGERANYL
DIPHOSPHATE SYNTHASE 1 affect chloroplast
development in Arabidopsis
thaliana.American
Journal of Botany 100(10): 2074-2084.
Luesse,
DR, Schenck, CA, Berner, BK, Justus, B, Wyatt, SE (2010)
GPS4 is allelic to ARL2: Implications for gravitropic
signal transduction. Gravitational and Space Biology 23:
95-96.
Luesse,
DR, DeBlasio, SL, Hangarter RP (2010) Integration
of phot1, phot2, and PhyB signalling in light-induced
chloroplast movements. Journal of Experimental
Botany. 61: 4387-4397.
Luesse,
DR, DeBlasio, SL, Hangarter RP (2006) Plastid Movement
Impaired 2 (PMI2 a new gene
required for normal blue-light-induced chloroplast
movements in Arabidopsis thaliana. Plant
Physiology. 141: 1328-1337.
DeBlasio
SL, Luesse DR, Hangarter RP (2005) A plant-specific
protein essential for blue-light-induced chloroplast
movements. Plant Physiology. 139: 101-114
DeBlasio
SL, Mullen JL, Luesse DR, Hangarter RP (2003)
Phytochrome modulation of blue light-induced chloroplast
movements in Arabidopsis. Plant Physiology. 133:
1471-1479
Stowe-Evans
EL, Luesse DR, Liscum E (2001) The enhancement of
phototropin-induced phototropic curvature in arabidopsis
occurs via a photoreversible phytochrome A-dependent
modulation of auxin responsiveness. Plant Physiology
126: 826-834
Harper
RM, Stowe-Evans EL, Luesse DR, Muto H, Tatematsu K,
Watahiki MK, Yamamoto K, Liscum E (2000) The NPH4 locus
encodes the auxin response factor ARF7, a conditional
regulator of differential growth in aerial Arabidopsis
tissue. Plant Cell 12: 757-770