Water-use adaptation through the barley circadian clock

Water availability constrains cereal production and its instability will increase with climate change. In the UK, cereal production must contend with drought one year and flooding the next. Numerous studies have examined stress-tolerance mechanisms in plants, which have been exploited to breed better varieties. Recent evidence suggests that plant growth, development and stress response are regulated by the circadian clock (Sanchez et al. 2010). This endogenous biological clock allows plants to dynamically predict expected environment changes to appropriately phase gene expression, metabolism and physiology (Muller et al. 2014).

Barley clock genes have been identified. This provides a foundation to examine how this drought resistant cereal uses its clock. Ppd-H1 and EAM8 are major photoperiod genes and our recent work showed that they manage osmotic stress tolerance (Habte et al. 2014). Using a diverse collection of barley landraces from drought prone areas, and a recently developed method to measure clock rhythms in a non-GM way (Gould et al. 2009), we can characterise clock performance in responses to water challenges in a large number of plants. This project will use i) diverse barley lines, ii) segregating populations, and iii) barley clock mutants to investigate how allelic variation in the clock impacts circadian control of stress adaptation, with a particular focus on water-use, and associate that to yield potential.

Workplan

The student will analyse natural genetic variation of central clock genes from the barley collection. Accessions carrying encoded amino-acid changes will be tested for alterations in diurnal transcript abundance. Different haplotypes, and their expression patterns, will be compared with geographic origin to gain insights into adaptive evolution. Barley lines showing differences in diurnal rhythms will be used to establish new mapping populations to determine the chromosomal position of clock controlling QTLs. New TILLING mutants at barley clock genes will be used to investigate adaptive significance of this clock. Relevant barley accessions will be grown under a range of abiotic stress conditions in greenhouse and field trials. The effects on adaptation in the various induced and natural mutants will be assessed by measuring plant height, flowering time, biomass and grain yield, as well as physiological traits such as stomatal conductance, photosynthetic rate and chlorophyll content.
To test whether candidate genes for abiotic stress tolerance are subject to diurnal regulation in barley, the expression of these genes will be analysed from samples collected throughout the day. Comparison of expression patterns in different TILLING lines and natural clock variants will demonstrate how phase shifts influence the expression of drought tolerance genes. Differences in diurnal rhythms on agronomic performance in different natural environments, at field sites at Stockbridge, will be tested by growing TILLING lines, one mapping population and selected diverse barley lines. These field experiments will further test how clock genes play a role in stress adaptation, such as drought or flooding. Evaluating performance thus reveals how the clock mediates water-stress responses.