Transcriptomic analysis supports the role of CATION EXCHANGER 1 in cellular homeostasis and oxidative stress limitation during cadmium stress

Investigation of genetic determinants of Cd tolerance in the Zn/Cd hyperaccumulator Arabidopsis halleri allowed the identification of the vacuolar Ca2+/HC exchanger encoding CAX1 gene. CAX1 was proposed to interfere with the positive feedback loop between Reactive Oxygen Species (ROS) production and Cd-induced cytosolic Ca2+ spikes, especially at low external Ca2+ supply. In this study expression of genes involved in ROS homeostasis, cell wall composition, apoplastic pH regulation and Ca2+ homeostasis were monitored in Arabidopsis thaliana wild-type and cax1-1 knock-out mutant and in Arabidopsis halleri wildtype exposed to cadmium or in control conditions. Clustering the outputs of the expression analysis in a gene co-expression network revealed that CAX1 and genes involved in Ca2+ cellular homeostasis, apoplastic pH and oxidative stress response were highly correlated in A. thaliana, but not in A. halleri. Many of the studied genes were already highly expressed in A. halleri and/or their expression was not modified by exposure to Cd. The results further supported the role of CAX1 in the regulation of cytosolic ROS accumulation as well as the existence of different cell wall modifications strategies in response to Cd in Arabidopsis thaliana and halleri.