Natural variation and genetic constraints on drought tolerance.

Drought is a central abiotic stress for both natural plant populations and agricultural crops. Substantial natural genetic variation in drought resistance traits has been identified in plant populations, crop species, and laboratory model systems. In particular, studies in Arabidopsis thaliana have discovered variation in a number of key physiological traits involved in plant-water relations that may underlie evolved drought stress responses among accessions. Despite this abundant variation, we still know little about the complex genetic architecture of drought tolerance or its role in constraining evolution. Unfortunately, few natural allelic variants have been cloned for drought related traits--progress cloning QTL, the use of RNA-sequencing methods for evaluating gene expression responses to soil drying, and improved methodology for exploring complex multivariate data all hold promise for moving the field forward. In particular, a better understanding of the molecular nature of pleiotropic gene action and the genetics of phenotypic plasticity will give insight into local adaptation in plants and provide new avenues for improving crops.