Gravitational and magnetic field variations synergize to cause subtle variations in the global transcriptional state of Arabidopsis in vitro callus cultures

Using diamagnetic levitation, we have exposed A. thaliana in vitro callus cultures to five environments with different levels of effective gravity (from levitation i.e. simulated mg* to 2g*) and magnetic fields (10.1 to 16.5 Tesla) and we have compared the results with those of similar experiments done in a Random Position Machine (simulated micro g) and a Large Diameter Centrifuge (2g) free of high magnetic fields. Microarray analysis indicates that there are changes in overall gene expression of the cultured cells exposed to these unusual environments but also that gravitational and magnetic field produce synergic variations in the steady state of the transcriptional profile of A. thaliana. Significant changes in the expression of structural, abiotic stress and secondary metabolism genes were observed into the magnet field. These results confirm that the strong magnetic field, both at micro g* or 2g*, has a significant effect on the expression of these genes but subtle gravitational effects are still observable. These subtle responses to microgravity environments are opposite to the ones observed in a hypergravity one.