Molecular Regulatory Mechanism of Exogenous Hydrogen Sulfide in Alleviating Low-Temperature Stress in Pepper Seedlings

Pepper (Capsicum annuum L.) is sensitive to low temperatures, with low-temperature stress affecting its plant growth, yield, and quality. In this study, we analyzed the effects of exogenous hydrogen sulfide (H(2)S) on pepper seedlings subjected to low-temperature stress. Exogenous H(2)S increased the content of endogenous H(2)S and its synthetase activity, enhanced the antioxidant capacity of membrane lipids, and protected the integrity of the membrane system. Exogenous H(2)S also promoted the Calvin cycle to protect the integrity of photosynthetic organs; enhanced the photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and photosynthesis; and reduced the intercellular CO(2) concentration (Ci). Moreover, the activities of superoxide dismutase, peroxidase, catalase, and anti-cyclic glutathione (ASA-GSH) oxidase were improved to decompose excess reactive oxygen species (ROS), enhance the oxidative stress and detoxification ability of pepper seedlings, and improve the resistance to low-temperature chilling injury in ‘Long Yun2’ pepper seedlings. In addition, the H(2)S scavenger hypotaurine (HT) aggravated the ROS imbalance by reducing the endogenous H(2)S content, partially eliminating the beneficial effects of H(2)S on the oxidative stress and antioxidant defense system, indicating that H(2)S can effectively alleviate the damage of low temperature on pepper seedlings. The results of transcriptome analysis showed that H(2)S could induce the MAPK-signaling pathway and plant hormone signal transduction; upregulate the expression of transcription factors WRKY22 and PTI6; induce defense genes; and activate the ethylene and gibberellin synthesis receptors ERF1, GDI2, and DELLA, enhancing the resistance to low-temperature chilling injury of pepper seedlings. The plant–pathogen interaction was also significantly enriched, suggesting that exogenous H(2)S also promotes the expression of genes related to plant–pathogen interaction. The results of this study provide novel insights into the molecular mechanisms and genetic modifications of H(2)S that mitigate the hypothermic response.