The circadian clock and stress adaptation in barley
Final Report Abstract
The circadian clock is an internal time-keeping mechanism that anticipates daily and seasonal changes in the environment. The prevalence of circadian rhythms in all domains of life suggests that circadian clocks provide an adaptive advantage for organisms and the circadian clock has been proposed as a key target for crop improvement. However, the effect of the clock on growth, yield and stress adaptation of major cereal crops are not well understood. The important cereal crop barley represents an ideal model to study the effect of the clock on adaptation to different environments, because the barley gene pool harbors large genetic variation and wild and landrace barley accessions grow in stress-prone areas. The overall objectives of the proposed project were to elucidate the adaptive significance of variation in the circadian clock in barley and 2) to gain a mechanistic understanding of the barley circadian clock and its interrelationship with growth and abiotic stress. Specifically, we proposed to 1) screen a wild and a landrace barley collection for variation in clock parameters and link this to eco-geographic conditions at the location of origin and 2) use identified clock variants to define output traits of the clock and input pathways into the clock by testing the plasticity of the clock in response to abiotic stresses. Using a high-throughput system to measure circadian rhythmicity based on changes in fluorescence we found that wild and landrace barley displayed wide variation in circadian parameters. In addition, the period time in wild and landrace barley genotypes was correlated to temperature at the site of origin, suggesting that circadian rhythms are under natural selection. Further we could demonstrate that the clock is plastic under abiotic stresses and displays changes in the period and amplitude. Clock mutants with a short circadian period were early flowering and had higher spike number and overall yield in rainfed field environments making the clock an interesting target for breeding in Mediterranean environments. Based on global transcriptome analyses we could show that about one third of the barley transcriptome is circadian controlled, while changes in the clock do not have a strong impact on transcript oscillations under day-night conditions. While Arabidopsis clock mutants are compromised in growth, we found that the clock does not affect biomass accumulation in barley. This is presumably because depletion of the major storage carbohydrate sucrose is not clock controlled while the degradation of starch, the major storage sugar in Arabidopsis is. Taken together our collaborative efforts have demonstrated that there is wide circadian variation in barley and this variation is presumably adaptive. While barley clock components are conserved between Arabidopsis and barley and also one third of the global transcriptome is under circadian control, output traits differ. Barley clock mutants are not obviously impaired in growth. Clock mutants show early flowering and improved yield under stress-conditions and are therefore valuable genetic material for breeding barley adapted to stress-prone environments.
Publications
- (2012) Expression conservation within the circadian clock of a monocot: natural variation at barley Ppd-H1 affects circadian expression of flowering time genes, but not clock orthologs. BMC Plant Biol. 12:97
Campoli C, Shtaya M, Davis S, von Korff M
(See online at https://doi.org/10.1186/1471-2229-12-97) - (2012) Mutation at the Circadian Clock Gene EARLY MATURITY 8 Adapts Domesticated Barley (Hordeum vulgare) to Short Growing Seasons. Proceedings of the National Academy of Sciences 109 (21), 8328-8333
Faure S, Turner AS, Gruszka D, Christodoulou V, Davis SJ, von Korff M, Laurie DA
(See online at https://doi.org/10.1073/pnas.1120496109) - (2013) HvLUX1 is a candidate gene underlying the early maturity 10 locus in barley: phylogeny, diversity, and interactions with the circadian clock and photoperiodic pathways. New Phytologist 199(4):1045-59
Campoli C, Pankin A, Casao CM, Davis SJ, von Korff M
(See online at https://doi.org/10.1111/nph.12346) - (2013) Osmotic stress at the barley root affects expression of circadian clock genes in the shoot. Plant Cell & Environment 37,1321–1337
Habte E, Müller L, Shtaya M, Davis SJ, von Korff M
(See online at https://doi.org/10.1111/pce.12242) - (2014) Connections between circadian clocks and carbon metabolism reveal species-specific effects on growth control. J. Exp. Bot 65(11):2915-23
Müller L, von Korff M, Davis SJ
(See online at https://doi.org/10.1093/jxb/eru117) - (2014) Mapping-by-sequencing identifies HvPHYTOCHROME C as a candidate gene for the early maturity 5 locus modulating the circadian clock and photoperiodic flowering in barley. Genetics
Pankin A, Campoli C, Dong X, Kilian B, Sharma R, Himmelbach A, Saini R, Davis SJ, Stein N, Schneeberger K and M von Korff
(See online at https://doi.org/10.1534/genetics.114.165613) - (2015) Detecting genetic diversity among barley landraces grown in the West-Bank. Journal of Animal and Plant Sciences, 25 (5): 1365-1370
Shtaya MJY, Abdallah J, Al-Fares H, Abu-Qaoud H, Baker OA, von Korff M, Haddad M
- (2016). The impact of domestication on the circadian clock. Trends in Plant Science 21:281-83
Shor E and Green RM
(See online at https://doi.org/10.1016/j.tplants.2016.01.022) - (2017) Correlations between circadian rhythms and growth in challenging environments. Plant Physiol. 173, 724-1734
Dakhiya Y, Hussien D, Fridman E, Kiflawi M, Green R
(See online at https://doi.org/10.1104/pp.17.00057)
