PARENT SESSION
Oral Session #17: Plant Ecology: Water Relations.
Presiding: W. Pockman
Monday, August 5. 1:00 PM to 3:45 PM. Coconino Meeting Room, TCC.

Genetics of drought adaptation in Arabidopsis thaliana: Natural variation, QTL mapping, near-isogenic lines and transformants.

McKay, John^*,1,2, Richards, James¹, Mitchell-Olds, Thomas², ¹ UC Davis, Davis, CA² Max-Planck-Institute for Chemical Ecology, Jena, Germany

ABSTRACT- We examined patterns of genetic variance and covariance in a range of traits thought to be involved in responses to local water availability, including time to flowering (drought escape) and stable carbon isotope ratio, d13C (dehydration avoidance). A greenhouse screening of genotypes of Arabidopsis thaliana native to habitats spanning a wide range of climatic conditions revealed significant genetic variation in both traits. An examination of the climate to which these genotypes are native shows that natural variation in d13C is correlated with differences in precipitation. We also found a large, highly significant positive genetic correlation (r_G = 0.98) between d13C and flowering time. This large correlation suggests the presence of a genetically based tradeoff between mechanisms of drought escape (early flowering) and dehydration avoidance (d13C). A positive correlation between time to flowering time and drought tolerance traits has also been found in annual crops such as barley, beans and wheat. We used candidate genes, QTL mapping, near-isogenic lines and over-expression to test for pleiotropy in the form of positive mutational covariance between d13C and flowering time. Screening of 8 physiological mutants showed variation in d13C but not flowering time. However QTL mapping and subsequent near-isogenic line analysis provide strong evidence for pleiotropic effects at FRIGIDA and FLC, loci known to be responsible for natural variation in flowering time. Our data suggest that naturally occuring genetic variation in flowering time may be caused by selection on alleles that alter stomatal transpiration and CO₂ assimilation. In addition our QTL analysis provide insight into the genomic regions which effect natural variation, both for individual ecophysiological traits and their joint distributions.

KEY WORDS: drought adaptation, water use efficiency, quantitative trait locus, pleiotropy