The specificity of calcium signature decoding mechanisms in their regulation of transcript and protein expression in Arabidopsis thaliana

Abstract

Calcium is a secondary messenger involved in many aspects of plant physiology and development. During stress, calcium concentration rapidly increases in the cytosol, triggering appropriate changes in downstream expression. It has been suggested that different calcium signatures regulate particular genes, transcription factors and cis elements. The ‘calcium signature’ hypothesis suggests that the calcium signatures themselves hold the information required for an appropriate response in the form of oscillations and/or other spatial, temporal patterns.
One of the main aims of this study was to investigate calcium signature kinetics and test them against known calcium-regulated cis elements. To identify novel calcium signatures, calcium responses were generated from single or combined calcium agonists. Luciferase assays were used to investigate novel calcium signature regulation of specific cis elements. Results suggested that individual calcium signatures regulated different cis elements specifically, with the expression kinetics changing when two cis elements were coupled. Further analysis suggested that some novel signatures occurred in different cell types at different times resulting in subsequent, polyphasic downstream expression kinetics. Furthermore, when a calcium signature was regulated by the circadian clock the downstream expression kinetics were altered depending on subjective time of day.
Investigations to date have concentrated on cytosolic calcium signature specificity in respect to the regulation of genes, with relatively little focus on protein regulation. I identified and characterised proteins whose levels either increased or decreased in response to a cytosolic calcium signature generated by mastoparan. It was seen that the proteins identified varied in function and abundance between timepoints, with a relatively high proportion involved in protein modification.