gene expression in gravitational and mechanically stimulated Arabidopsisroots in order
to identify specificity and analyze temporal resolution for the very early responses to
these stimuli at the molecular level (Kimbrough et al. 2004; Chapter 2). Transgenic
plants modified in their activation of a very early signaling molecule [inositol-1,4,5-
triphosphate (InsP 3 )] were generated and showed a decreased and delayed response to
gravity as well as an increased tolerance to other abiotic stresses (Salinas-Mondragon et
al. 2005; Perera et al. 2006). Although Arabidopsisserves as an excellent model system,
its behavior does not always predict the behavior of crop plants. The genetic differences
between plant species that have evolved over millions of years and crop plants obtained
by targeted breeding do not always allow for a direct translation of phenotypic effects of
biotechnological manipulation. For example, tomato plants transformed with the same
gene used to reduce InsP 3 -mediated signaling in Arabidopsis(discussed above) exhibit
extreme drought-tolerance and have a very high stress-tolerant phenotype overall (Perera
et al., in preparation; Khodakovskaya et al., in preparation)—phenotypes not readily pre-
dicted from the known effects of the transgene in Arabidopsis.
Conceptual designs for greenhouses on Mars, on the Moon, and in Earth orbit incor-
porate artificial light, altered gravity, and low atmospheric pressure and composition,
all of which are known to affect plant physiology and development (McKay et al. 1991;
Corey et al. 2002). If plants can be developed that can thrive at less than Earth atmos-
pheric pressures, then this will save on the materials and energy costs to build and
maintain a “Martian” greenhouse. Using a low-pressure growth chamber, Paul et al.
(2004) compared gene expression, as changes in transcript abundance, between wild-
typeArabidopsisplants grown under Earthlike atmospheric pressure (101 kPa), low at-
mospheric pressure (10 kPa), and low oxygen concentration (2% O 2 at 101 kPa). They
identified genes regulated specifically by hypobaria or hypoxia, and genes regulated by
both stresses. Under hypobaria, the most dramatic changes were found in desiccation-
associated and abscisic acid-regulated pathways, indicating water stress (Paul et al.
2004). These kinds of assays suggest that plants which evolved on Earth do possess the
genetic resources to become adapted to a Martian greenhouse environment.
Genetic engineering is now routine for some plant species. Insertion of a single gene
or a cluster of genes results in transgenic plants expressing new phenotypic traits.
Examples include resistance to insects (Bt corn), resistance to high salt, improved toler-
ance to chilling, ozone resistance, altered starch concentration and composition, altered
lipid composition, enhanced shelf life (Stitt and Sonnewald 1995; Giddings et al. 2000;
Daniell et al. 2001; Qi et al. 2004; Khodakovskaya et al. 2006), enhanced vitamin and an-
tioxidant content (Shintani and DellaPenna 1998; Ye et al. 2000; Davuluri et al. 2005),
production of edible vaccines and pharmaceuticals (Walmsley and Arntzen 2000; Ma et
al. 2005), and production of thermoplastics and industrial oils (Jaworski and Cahoon
2003). Recently the successful expression of an active archaebacterial superoxide reduc-
tase from the thermophile Pyrococcus furiosusin plant cells opened up an entire new
array of possibilities to generate stress-tolerant plants (Im et al. 2005). The use of genes
from extremophiles that have evolved to survive the most extreme physical environments
can now be used to greatly extend the adaptive range of successful crop plants for space
environments (Grunden and Boss 2004).
frankie
(Frankie)
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