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Department of Plant Sciences

 

NERC/UF

Supervisor: Professor Julia Davies

 

Soil salination is an increasing threat to plant life and there is an urgent need to understand how plant roots perceive this stress and adapt to it. At sub-lethal dose, Na+ perception causes a cytosolic calcium signal to propagate from the roots to trigger leaf adaptation. Primary root and root hair growth are inhibited and lateral roots may emerge. The primary root may also exhibit halotropism, growth away from a saline hotspot, as an escape response.  Inhibition of root growth and reduced plant fitness are exacerbated by the sub-optimal levels of phosphate found in many soils. Thus it is also important to understand how phosphate deprivation and salinity stress modulate adaptive outcomes. There is a significant gap in our knowledge about root hairs. When delivered as single stresses, phosphate deprivation promotes root hair growth as a key adaptation but salinity stress is suppressive. There are no reports on the effect of the combined stresses; could an ecotype still grow root hairs under salinity stress? Likewise the effect of phosphate deprivation on halotropism remains untested, as do stress response pathways. This project aims to fill those knowledge gaps.

The project builds on the Davies lab’s work on root hair growth, salinity stress signalling and abiotic stress signalling under phosphate deprivation. The project has three objectives, in line with the NERC plant science remit of stress responses. 1. Examine the effect of combined salinity stress and phosphate deprivation on root hair growth and halotropism of Arabidopsis ecotypes to identify key underpinning genes. 2. Determine whether halotropism involves calcium signalling. 3. Determine whether Arabidopsis ecotypes vary in the salt-induced calcium signal as a function of phosphate nutrition and whether this influences the adaptive response of leaves.

For objective 1, the workplan will be based on previous studies of single and double salinity stress/phosphate deprivation factorial experiments on root system architecture using a wide range of ecotypes to determine effects on root hair proliferation and growth. Phenotypes will form the basis of genome-wide association mapping to identify key underpinning genes. For objective 2, the Arabidopsis ecotypes expressing a genetically-encoded cytosolic calcium reporter will be used to monitor changes in root cytosolic calcium during the halotropic response. Mutants in salinity sensing and signalling will be tested for aberrant responses. For objective 3, Arabidopsis ecotypes expressing a genetically-encoded cytosolic calcium reporter will be used to assess ecotype-specific salt-induced calcium signalling in roots as a function of phosphate nutrition. These signals will be compared to the transcriptional response of leaves for key salt-adaptive genes. Mutants in salinity sensing and signalling will also be tested.

 

References

  • van Zelm, E., Zang, Y. & Testerink, C. (2020) Salt Tolerance Mechanisms of Plants. Annual Review of Plant Biology 71, 403 - 433. doi.org/10.1146/annurev-arplant-050718-100005
  • Galvan-Ampudia, C.S., et al. (2013) Halotropism is a Response of Plant Roots to Avoid a Saline Environment. Current Biology 23, 2044 - 2050. doi.org/10.1016/j.cub.2013.08.042
  • Jiang, Z.H., et al. (2019) Plant Cell-surface GIPC Sphingolipids Sense Salt to Trigger Calcium Influx. Nature, 572, 341 - 346. doi.org/10.1038/s41586-019-1449-z
  • Matthus, E., et al. (2019) Phosphate Starvation Alters Abiotic-stress-induced Cytosolic Free Calcium Increase in Roots. Plant Physiology 179, 1754-1767. doi.org/10.1104/pp.18.01469