Cadmium Stress Disrupts Auxin Signaling and Growth in Ilex verticillata: Insights from Physiological and Transcriptomic Analyses

Cadmium (Cd) pollution poses significant threats to ecosystems and human health, with agricultural soils in China particularly affected. <i>Ilex verticillata</i>, a popular ornamental plant, has not been extensively studied for its response to Cd stress. This study investigated the physiological and molecular mechanisms underlying Cd stress tolerance in <i>I. verticillata</i>, focusing on auxin signaling pathways. Under Cd stress (500 mmol/kg soil), <i>I. verticillata</i> exhibited inhibited stem growth, reduced photosynthetic capacity, and elevated oxidative stress markers such as malondialdehyde, H₂O₂, ·O₂^-, and antioxidant enzyme activities. Transcriptomic analysis revealed 3750 differentially expressed genes (DEGs) with significant enrichment in auxin signaling pathways. Six nucleus-localized <i>IvIAA</i> genes were identified and shown to interact with the transcription factor IvMYB77, suggesting a regulatory module in Cd stress responses. These findings highlight the role of auxin signaling in mediating Cd stress tolerance and provide insights into the molecular adaptation of <i>I. verticillata</i> to heavy metal pollution.