An Ancestral Allele of Promotes Proline Accumulation and Drought Adaptation in Cultivated Barley.

Water scarcity is a critical threat to global crop production. Here, we used the natural diversity of barley () to dissect the genetic control of proline (Pro) mediated drought stress adaptation. Genetic mapping and positional cloning of a major drought-inducible quantitative trait locus () revealed unique allelic variation in () between the cultivated cultivar Scarlett (ssp. ) and the wild barley accession ISR42-8 (ssp. ). The putative causative mutations were located in the promoter of across the DNA binding motifs for abscisic acid-responsive element binding transcription factors. Introgression line (IL) S42IL-143 carrying the wild allele of showed significant up-regulation of expression compared to Scarlett, which was consistent with variation in Pro accumulation under drought. Next, we transiently expressed promoter::reporter constructs of ISR42-8 and Scarlett alleles in Arabidopsis () mesophyll protoplasts. GUS expression analysis showed a significantly higher activation of the ISR42-8 promoter compared to Scarlett upon abscisic acid treatment. Notably, the ISR42-8 promoter activity was impaired in protoplasts isolated from the loss-of-function quadruple mutant. A series of phenotypic evaluations demonstrated that S42IL-143 maintained leaf water content and photosynthetic activity longer than Scarlett under drought. These findings suggest that the ancestral variant of has the potential for drought tolerance and understanding drought physiology of barley and related crops.