Cadmium (Cd) has a detrimental effect on living organisms. Due to their similar physical properties, Cd can compete with other divalent metal ions, such as iron (Fe) and zinc (Zn), during uptake by roots from soils. 

In a recent study published in Journal of Integrative Plant Biology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences revealed that the transcription factor bHLH104 positively regulates Cd tolerance in Arabidopsis thaliana. 

Given that Cd exposure can cause Fe-deficiency symptoms in plants, the researchers tested whether Cd stress affected Fe uptake and accumulation in plants.

They found that Cd treatment interfered with Fe distribution between roots and shoots, which may be one of the reasons Cd exposure causes Fe-deficiency symptoms. 

To further assess the function of bHLH104 in Cd tolerance, the growth of wild type and the bHLH104 loss-of-function mutants was analyzed under Cd exposure. 

Considering that loss of function of bHLH104 resulted in reduced expression of Fe deficiency-responsive genes, the researchers inquired whether overexpression of bHLH104 would enhance the Fe-deficiency response under Cd stress conditions. 

They also analyzed the phenotypes of bHLH104 overexpression plants grown on medium with or without Cd.  

The results showed that overexpression of bHLH104 enhanced the expression of Fe deficiency-responsive genes and causes Fe over-accumulation.

They also showed that bHLH104 overexpression promoted the expression of heavy metal detoxification-associated genes and facilitated Cd sequestration in the roots. 

The identification of bHLH104 as a positive regulator of Cd tolerance suggests that it could be used in new strategies to engineer crops for adaptation to Cd stress.