# Sesuvium portulacastrum SpC3H Enhances Salt Tolerance of Arabidopsis thaliana by Regulating Lignin Synthesis and Scavenging Reactive Oxygen Species

## TL;DR

A gene from a salt-tolerant plant helps Arabidopsis survive salt stress by boosting lignin production and reducing harmful oxygen species.

## Contribution

The study identifies SpC3H's role in salt tolerance through lignin synthesis and ROS scavenging in a halophyte.

## Key findings

- SpC3H expression increases significantly in roots and leaves under salt stress.
- Transgenic Arabidopsis with SpC3H showed improved growth and reduced ROS under salt stress.
- SpC3H enhances lignin biosynthesis and antioxidant enzyme activity in plants.

## Abstract

Lignin constitutes a fundamental component of plant defense mechanisms against environmental stressors. 4-coumarate 3-hydroxylase (C3H) serves as a pivotal enzyme in lignin biosynthesis. However, its role in the halophyte Sesuvium portulacastrum remains uncharacterized. In this study, the SpC3H gene was cloned, and subsequent sequence alignment and phylogenetic analyses revealed the highest similarity (57.14%) with BvC3H from Beta vulgaris, exhibiting the closest evolutionary relationship with Beta vulgaris and Spinacia oleracea C3H protein. Quantitative real-time polymerase chain reaction demonstrated that SpC3H expression was markedly upregulated in both roots and leaves of S. portulacastrum under 800 mM NaCl treatment. Root expression peaked at 48 h (25.3-fold), whereas leaves displayed dual expression maxima at 12 h (7.9-fold) and 72 h (10.7-fold). Subcellular localization assays confirmed cytoplasmic distribution. Heterologous expression in Arabidopsis thaliana indicated that transgenic lines exhibited enhanced growth performance, higher fresh weight, and elevated lignin contents relative to wild-type plants under salt stress, accompanied by reduced reactive oxygen species (ROS) accumulation and lower relative electrical conductivity. Furthermore, activities of superoxide dismutase and peroxidase, together with expression of lignin biosynthesis-associated and antioxidant enzyme genes, were markedly elevated. Collectively, these findings establish that SpC3H confers salt tolerance by promoting lignin biosynthesis and activating antioxidant defenses to eliminate ROS, thereby providing a theoretical foundation for genetic improvement of plant salt tolerance.