Methane alleviates alfalfa cadmium toxicity via decreasing cadmium accumulation and reestablishing glutathione homeostasis

Abstract

Although methane (CH₄) generation triggered by some environmental stimuli, displays the protective response against oxidative stress in plants, whether and how CH₄ regulates plant tolerance against cadmium stress is largely unknown. Here, we discovered that cadmium (Cd) stimulated the production of CH₄ in alfalfa root tissues. The pretreatment with exogenous CH₄ could alleviate seedling growth inhibition. Less amounts of Cd accumulation was also observed. Consistently, in comparison with Cd stress alone, miR159 transcript was down-regulated by CH₄, and expression levels of its target gene ABC transporter was increased. By contrast, miR167 transcript was up-regulated, showing a relatively negative correlation with its target gene Nramp6. Meanwhile, Cd-triggered redox imbalance was improved by CH₄, evidenced by the reduced lipid peroxidation and hydrogen peroxide accumulation, as well as the induction of representative antioxidant genes. Further results showed that Cd-triggered decrease of the ratio of reduced/oxidized (homo)glutathione was rescued by CH₄. Additionally, CH₄-triggered alleviation of seedling growth was sensitive to a selective inhibitor of glutathione biosynthesis. Overall, above results revealed that CH₄-alleviated Cd accumulation at least partially, required the modulation of heavy metal transporters via miR159 and miR167. Finally, the role of glutathione homeostasis elicited by CH₄ was preliminarily suggested.

Keywords: Cadmium stress; Cd transporter; Glutathione homeostasis; Medicago sativa; Methane.