The mechanism and application of the selenium hyperaccumulator <i>Cardamine hupingshanensis</i> : status and challenges

Cardamine hupingshanensis is a selenium (Se) hyperaccumulating plant discovered in 2008 in China. This comprehensive review summarizes the state-of-the-art progress on the molecular mechanisms underlying Se hyperaccumulation in C. hupingshanensis. The direct mechanisms encompass the key genes involved in the Se accumulation, localization and transformation processes in the plant. Homocysteine S-methyltransferase (HMT) and methionine S-methyltransferase (MMT) may contribute to Se hyperaccumulation in C. hupingshanensis, supported by the detection of selenolanthionine in the water extraction fraction, and selenocystine and selenomethylcysteine in the proteolytic hydrolysate fraction. Indirect mechanisms, such as structural adaptations, sequestration/transportation, sulphur conservation, oxidative stress control, protein degradation and interactions with rhizosphere/endophytic microbiota, may also contribute to its Se hyperaccumulation. This review also explores the applications of Se biofortification and phytoremediation, highlighting the potential of C. hupingshanensis in enhancing Se content in crops and remediating Se-contaminated environments. Further investigation is needed into the challenges related to C. hupingshanensis, focusing on the pathways and processes of Se accumulation and transport within the rhizosphere soil-plant-air system, comparative studies that have used a multi-omics strategy to delve deeper into the molecular mechanisms of Se hyperaccumulation under various Se speciation treatments, the role of core microbiota, potential applications in food processing and agriculture, and the synergistic remediation of Se and other heavy metal contaminants.