MAPK-Dependent Copper Tolerance Mechanisms Revealed by Integrated Physiology and Transcriptomics in Peanut

Xuefeng Bao¹ZhiQiang Gao¹Weimin Ning¹Mian Hu¹Xuan Dong^2*

• ¹Xichang University, Xichang, China
• ²Xuchang University, Xuchang, China

In order to elucidate the physiological and molecular responses of peanut (Arachis hypogaea L. c.v. 'Haihua No. 1') to copper stress, this study exposed seedlings to 0 (control) or 50 mg/L CuSO₄ solution, with three biological replicates for each treatment. We quantitatively measured root length and biomass, tissue contents of eight ions (K⁺, Na +, Mg2+, Ca2+, Fe3+, Mn2+, Cu2+, Zn2+), secondary oxidative stress indices, and the activities of key antioxidant enzymes. Subsequently, RNA-seq and qPCR validation were performed to analyze transcriptional changes, with an aim to reveal specific gene-response modules in peanut seedling roots under copper stress. The results showed that copper stress strongly induces the expression of MPK4, a key nodal point within the MAPK pathway. Post-translationally, MPK4 is highly likely to phosphorylate two critical protein classes: NAC and LBD. Within this unique regulatory network, NAC functions as a core transcription factor, directly regulating the transcription of copper defense-related genes. Concurrently, LBD directly down-regulates genes associated with lateral root growth. This action by LBD, through a reallocation of biological resources, indirectly promotes the increased expression of genes involved in GSH-dependent heavy metal detoxification and secondary oxidative stress (e.g., GST and POD), thereby cooperatively enhancing the plant's detoxification and antioxidant capacity. This study may provide theoretical support for the breeding of copper-tolerant peanut cultivars.