# Genome-Wide Thioredoxin System in Cardamine hupingshanensis: Role in Se Stress and Metabolism

## TL;DR

This study explores how the thioredoxin system in Cardamine hupingshanensis helps the plant handle selenium stress and metabolism, offering insights for improving selenium biofortification in crops.

## Contribution

The first genome-wide identification of the thioredoxin system in a selenium hyperaccumulator plant.

## Key findings

- 74 thioredoxin (TRX) genes and 12 thioredoxin reductase (TR) genes were identified in Cardamine hupingshanensis.
- ChTRX genes showed tissue-specific expression under selenium stress, with root-specific genes potentially mitigating oxidative damage.
- ChACHT4-1 interacts with key selenium metabolism enzymes, suggesting a role in redox regulation.

## Abstract

As a selenium hyperaccumulator plant, the role of the thioredoxin system in Cardamine hupingshanensis in selenium stress response and selenium metabolism remains unclear. Elucidating the function of this system is of important significance for understanding the mechanisms of plant selenium tolerance and optimizing selenium biofortification in crops. This study presents the first genome-wide identification of the thioredoxin system in C. hupingshanensis, aiming to investigate its functions under selenium stress and in selenium metabolism. In the present study, we identified 74 thioredoxin (TRX) genes and 12 thioredoxin reductase (TR) genes, which can be classified into different types and are widely distributed within cells. Under selenium stress, these genes exhibited tissue-specific expression patterns, and predictions suggest that some selenium stress-responsive genes regulate the redox processes of key enzymes involved in selenium metabolism. In summary, this study preliminarily demonstrates that the thioredoxin system in C. hupingshanensis may influence selenium metabolism through redox regulation, providing insights into the mechanisms of selenium tolerance in hyperaccumulator plants.

The thioredoxin system is crucial for maintaining redox balance and stress responses in plants, but its role in selenium hyperaccumulators remains poorly understood. To our knowledge, this study is the first to perform a genome-wide identification of the thioredoxin system in Se hyperaccumulator Cardamine hupingshanensis. We identified 74 ChTRX genes and 12 ChTR genes, among which ChTRX genes accounted for approximately 86.05% of the total identified thioredoxin system genes. Phylogenetic and structural analyses classified the ChTRXs into two types, typical (with the WCGPC active site) and atypical (with the XCXXC active site), with typical ChTRXs comprising about 48.65% and atypical ChTRXs about 51.35% of the total ChTRXs. Subcellular localization analysis revealed a diverse distribution, such as chloroplast, mitochondrion and cytoplasm. The chloroplast-localized ChTRXs are the most abundant, accounting for approximately 60% of all ChTRXs. Under Se stress, the expression of ChTRX genes exhibited significant tissue-specific differences: approximately 52.5% of ChTRX genes showed responsive expression in the roots, while only 31.25% responded in the leaves, suggesting that root-specific genes may play an important role in mitigating Se-induced oxidative damage. Through expression data and molecular docking analysis, we discovered that ChACHT4-1 can interact with the disulfide bonds of key Se metabolism related enzymes ChAPK and ChAPR, suggesting its potential reductive activity. Furthermore, we predicted stress-responsive ChTRXs regulated by multiple ChNTRs in TRX–TR regulatory pathway. Overall, our research indicates that the thioredoxin system influences Se metabolism in C. hupingshanensis through redox regulation, providing insights into the Se tolerance mechanisms of hyperaccumulating plants and offering perspectives for optimizing Se biofortification strategies in crops.