Ectopic expression of IMA small peptide genes confers tolerance to cadmium stress in Arabidopsis through activating the iron deficiency response

Increasing cadmium (Cd) pollution severely affects plant growth and development, posing risks to human health via food chains. The Cd toxicity could be mitigated by improving Fe nutrient in plants. IMA1 and IMA3, two novel small peptides functionally epistatic to the key transcription factor bHLH39 but independent of bHLH104, were recently identified as the newest additions to the Fe regulatory cascade, but their roles in Cd uptake and toxicity remain not addressed. Here, the functions of two IMAs and two transcription factors related to Cd tolerance were verified. Overexpression of either bHLH39 or bHLH104 in Arabidopsis showed weak roles in Cd tolerance, but overexpression of IMAs, which activates the Fe-deficient response, significantly enhanced Cd tolerance, showing greater root elongation, biomass and chlorophyll contents. The Cd contents did not show significant difference among the overexpression lines. Further investigations revealed that the tolerance of transgenic plants to Cd mainly depended on higher Fe accumulation, which decreased the MDA contents and enhanced root elongation under Cd exposure, finally contributing to attenuating Cd toxicity. Taken together, the results suggest that increasing Fe accumulation is promising for improving plant tolerance to Cd toxicity and that IMAs are potential candidates for solving Cd toxicity problem.