Researchers are hunting for drought tolerance genes in ancient Andean
landraces.
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 conditions.

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.

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