Thermal Stability of Barley Circadian Clock and Growth: A Tango of Two Genomes

Temperature compensation, expressed as the ability to maintain clock characteristics in face of temperature changes, i.e. robustness, is considered a key feature of circadian clock systems. In this study, we explore the genetic basis for lack of robustness, i.e. plasticity, of circadian clock as reflected by photosynthesis rhythmicity, under high temperatures. The clock rhythmicity of a new wild barley (Hordeum vulgare sps. spontaneum) reciprocal doubled haploid (DH) population was measured with a new platform (SensyPAM) that enables high throughput clock measurements. This analysis pointed to the prevalence of clock acceleration under high vs optimal temperature environments. Furthermore, genetic analysis using nuclear genotype-by-sequencing and chloroplast resequencing, included QxE and a unique binary-threshold models, indicated several major loci affecting stability including the plasmotype. Furthermore, analysis of the same DH population for life history traits show pleiotropic effects of cytoplasm and nuclear QTL on growth and reproductive output robustness thereby indicating adaptive value of this diversity. Notably, extending this analysis within cultivated background using the Halle Exotic Barley interspecific population indicates that some of these clock loci, which were not reported before, are consistent thereby suggesting their breeding potential. Developments of genome editing and allele mining approaches for identifying impact, and mechanism underlying, of specific nuclear loci and plasmotype variations on clock robustness and on whole-plant phenotype under changing environments will be discussed.