A cadmium stress-responsive gene AtFC1 confers plant tolerance to cadmium toxicity

Non-essential trance metal such as cadmium (Cd) is toxic to plants. Although some plants have developed elaborate strategies to deal with absorbed Cd through multiple pathways, the regulatory mechanisms behind the Cd tolerance are not fully understood. Ferrochelatase-1 (FC1, EC4.99.1.1) is the terminal enzyme of heme biosynthesis, catalyzing insertion of ferrous ion into protoporphyrin IX. Recent studies have shown that FC1 is involved in several physiological processes. However, its biological function associated with plant abiotic stress response is poorly understood.

In this study, we showed that AtFC1 was transcriptionally activated by Cd exposure. AtFC1 overexpression (35S::FC1) lines accumulated more Cd and non-protein thiol compounds than wild-type, and conferred plant tolerance to Cd stress, with improved primary root elongation, biomass and chlorophyll (Chl) content, and low degree of oxidation associated with reduced H₂O₂, O^·2- and peroxides. In contrast, the AtFC1 loss of functional mutant fc1 showed sensitivity to Cd stress. Exogenous provision of heme, the product of AtFC1, partially rescued the Cd-induced toxic phenotype of fc1 mutants by improving the growth of seedlings, generation of glutathione (GSH) and phytochelatins (PCs), and GSH/PCs-synthesized gene expression (e.g. GSH1, GSH2, PCS1, and PCS2). To investigate the mechanism leading to the AtFC1 regulating Cd stress response in Arabidopsis, a transcriptome of fc1 mutant plants under Cd stress was profiled. Our data showed that disfunction of AtFC1 led to 913 genes specifically up-regulated and 522 genes down-regulated in fc1 mutants exposed to Cd. Some of the genes are involved in metal transporters, Cd-induced oxidative stress response, and detoxification.

These results indicate that AtFC1 would act as a positive regulator of plant tolerance to Cd stress. Our study will broaden our understanding of the role of FC1 in mediating plant response to Cd stress and provide a basis for further exploration of its downstream genes.