June 20, 2008
American Society of Plant
Climate change is expected to
exacerbate drought events throughout the world, resulting in
large-scale ecosystem alteration and failure of
drought-sensitive crops. In addition, periods of drought vary
from year to year in severity and length, making it difficult
for plants to adapt to more severe conditions. Many modern
varieties of potatoes are considered to be drought-sensitive.
However, evolution and cultivation in the cold, dry Andean
Altiplano gave rise to a number of potato varieties that could
tolerate drought. Scientists are studying these varieties to
identify the genes and molecular mechanisms of drought tolerance
in order to engineer new drought-resistant crops of potato, as
well as other Solanaceous vegetables.
Dr. Roland Schafleitner and his colleagues, Raymundo Oscar
Gutierrez Rosales, Luz Rosalina Tincopa Marca, and Merideth
Bonierbale, are examining the genes for drought tolerance traits
in several native Andean potato landraces. Dr. Schafleitner, of
the Germplasm Enhancement and Crop Improvement Division,
International Potato Center in Peru, will be presenting this
work at a symposium on the Biology of Solanaceous Species at the
annual meeting of the American Society of Plant Biologists in
Mérida, Mexico (June 29, 8:30 AM).
From tiny dark blue tubers to huge tan bakers, potatoes come in
an astonishing variety of colors and sizes, reflecting their
genetic variety as well as their long history of cultivation.
Potato was first domesticated in the Peruvian Andes over 7,000
years ago and was carried to Europe in the late 16th century,
becoming such an important food source that a failure in the
crop caused by blight in Ireland triggered a famine. It is a
member of the Solanaceae or nightshade family, which also
includes tomato, eggplant, tobacco, and chili peppers.
Drought first causes stomatal closure, reducing CO2 uptake for
photosynthesis, reducing plant growth and yield. Plants vary in
the types and speed of responses to drought conditions,
depending on their genetic and ecotypic backgrounds, but a
number of drought responsive genes are conserved across plant
taxa, especially genes involved in osmotic adjustment,
detoxification, and cell communication and signaling.
Schafleitner and his co-workers studied two Andean potato
clones, SA2563 and Sullu (Solanum tuberosum) L. subsp. Andigena
(Juz, Bukasov) under field conditions and used microarrays to to
identify genes that are up- and down-regulated under drought
The scientists identified about 2000 genes that were
differentially regulated under drought conditions. Many of these
genes contribute to the increased drought tolerance of the two
clones under investigation. Up-regulated genes included
transcription factors and cell signaling-related genes such as
kinases and phosphatases, which regulate numerous functions,
including metabolic changes and cell defense functions. Solute
concentrations were increased, lowering osmotic potential, to
induce uptake of water from drying soils. Increased expression
of lipid transfer genes and fatty-acid and wax synthase genes
suggested the reinforcement of cell membranes and cuticles.
Genes for cell wall components were also upregulated, as were
biosynthetic genes for antioxidants such as flavonoids and
anthocyanins, which function in cell protection and
detoxification under oxidative stress Many of the ancient potato
landraces were adaptations to different environmental conditions
such as different soils, temperature, altitude, and drought.
Preservation of these varieties and knowledge of their genetic
and adaptive histories are of paramount importance as farmers
around the world cope with changes in temperature and water
availability and struggle to maintain a food supply for growing
populations. The International Potato Center in Lima, Peru
maintains the world’s largest collection of tubers in the
interest of conserving the genetic diversity of potato as well
as investigating traits such as resistance to various insects
and diseases, as well as to cold, heat and drought. The results
of this research are used for screening and breeding efforts in
crop improvement. The knowledge gained from these efforts can
also be applied in crop and yield improvement efforts for other
members of the Solanaceae.