# MAPK-dependent copper tolerance mechanisms revealed by integrated physiology and transcriptomics in peanut

## TL;DR

This study explores how peanut plants respond to copper stress, revealing key genes and mechanisms that could help breed copper-tolerant varieties.

## Contribution

The study identifies MPK4, NAC, and LBD as key regulators in peanut's copper stress response, offering new insights for breeding copper-tolerant cultivars.

## Key findings

- Copper stress significantly increased MPK4 gene expression in peanut seedlings.
- NAC and LBD proteins regulate copper defense genes and lateral root growth, enhancing detoxification and antioxidant capacity.
- The MPK4 pathway plays a central role in peanut's copper tolerance mechanisms.

## Abstract

To elucidate the physiological and molecular responses of peanut (Arachis hypogaea L L. c.v. ‘Haihua No. 1’) to copper stress, this study aimed to investigate the changes in root morphology, ion content, oxidative stress, and gene expression under copper stress conditions.

Seedlings were exposed to 0 (control) or 50 mg/L CuSO₄ solution, with three biological replicates for each treatment. Root length and biomass were measured quantitatively, along with tissue contents of eight ions (K+, Na+, Mg2+, Ca2+, Fe3+, Mn2+, Cu2+, Zn2+), secondary oxidative stress indices, and activities of key antioxidant enzymes. RNA-seq and qPCR validation were performed to analyze transcriptional changes and identify specific gene-response modules in peanut seedling roots under copper stress.

Copper stress significantly induced the expression of MPK4, a key component of the MPK4 pathway. Post-translationally, MPK4 likely phosphorylated two critical protein classes: NAC and LBD. NAC functioned as a core transcription factor, directly regulating the transcription of copper defense-related genes. LBD directly down-regulated genes associated with lateral root growth, indirectly promoting the expression of genes involved in GSH-dependent heavy metal detoxification and secondary oxidative stress (e.g., GST and POD), thereby enhancing the plant's detoxification and antioxidant capacity.

This study provides insights into the regulatory mechanisms that peanut plants employ to cope with copper stress. The findings highlight the roles of MPK4, NAC, and LBD in the plant's response to copper stress and suggest that these genes could be targeted in breeding programs to develop copper-tolerant peanut cultivars. The results may provide theoretical support for the development of such cultivars.