Identification and characterization of QTL underlying whole-plant physiology in Arabidopsis thaliana:: δ13C, stomatal conductance and transpiration efficiency

Water limitation is one of the most important factors limiting crop productivity world-wide and has likely been an important selective regime influencing the evolution of plant physiology. Understanding the genetic and physiological basis of drought adaptation is therefore important for improving crops as well as for understanding the evolution of wild species. Here, results are presented from quantitative trait loci (QTL) mapping of flowering time (a drought escape mechanism) and carbon stable isotope ratio (delta C-13) (a drought-avoidance mechanism) in Arabidopsis thaliana. Whole-genome scans were performed using multiple-QTL models for both additive and epistatic QTL effects. We mapped five QTL affecting flowering time and five QTL affecting delta C-13, but two genomic regions contained QTL with effects on both traits, suggesting a potential pleiotropic relationship. In addition, we observed QTL-QTL interaction for both traits. Two delta C-13 QTL were captured in near-isogenic lines to further characterize their physiological basis. These experiments revealed allelic effects on delta C-13 through the upstream trait of stomatal conductance with subsequent consequences for whole plant transpiration efficiency and water loss. Our findings document considerable natural genetic variation in whole-plant, drought resistance physiology of Arabidopsis and highlight the value of quantitative genetic approaches for exploring functional relationships regulating physiology.