Low-temperature stress is a key environmental factor limiting the introduction and cultivation of plants native to tropical and subtropical regions; however, the molecular mechanisms governing their cold tolerance are not fully understood. In this study, we identified a core circadian rhythm gene-PiLUX-in the ornamental and medicinal plant Plumbago indica L. (P. indica) and systematically analyzed its role in the plant's response to low temperatures. Transcriptomic analysis and physiological measurements indicated that PiLUX is significantly upregulated following cold induction; furthermore, its transcriptional levels show positive correlations with cold-tolerance-related physiological indicators such as reactive oxygen species (ROS) scavenging capacity, osmoregulatory substance accumulation, and membrane lipid peroxidation. In transgenic Arabidopsis thaliana (A. thaliana), heterologous overexpression of PiLUX enhances cold tolerance but also delays flowering, suggesting that reproductive development is sacrificed to conserve nutrients for cold tolerance. VIGS experiments confirmed that PiLUX knockdown exacerbates oxidative damage in P. indica under cold stress and reduces its recovery ability. The experimental results and transcriptomic data suggest that PiLUX may participate in the low-temperature response downstream of, or in parallel with, the CBF pathway; however, direct regulatory evidence is still required. This study provides insights into the adaptation strategies of thermophilic plants under low-temperature stress and offers a theoretical basis and genetic resources for cold-tolerance breeding in P. indica.
