Brassinosteroid-mediated carotenoid regulation enhances chilling tolerance in pepper.

Background: Low temperature stress severely limits the growth and development of pepper (Capsicum annuum L.). Brassinolides (BRs) and carotenoids play key roles in alleviating low-temperature stress. At present, the research on the regulatory relationship between BRs and carotenoids remains rather limited. In this study, CaBZR1 (Brassinazole-Resistant 1), a key transcription factor of BR signaling pathway, and CaLCYB (Lycopene β-Cyclase), a carotenoid synthesis gene, were silenced using virus-induced gene silencing (VIGS) technology. The role of BR-mediated carotenoid regulation of cold tolerance was explored.

Results: The results showed that after silencing CaBZR1 and CaLCYB respectively, the carotenoid content, the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), as well as the chlorophyll fluorescence parameter (Fv/Fm) all decreased significantly. The levels of superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) increased significantly, leading to oxidative damage to membrane lipids. The expressions of cold-responsive genes such as CaFbox1 (F-box protein 1), CaMBF1 (Multiprotein Bridging Factor 1) and CaNAC3 (NAC domain containing protein 3) were significantly reduced. Exogenous spraying of EBR alleviated the damage in CaBZR1 and CaLCYB-silenced plants under low-temperature stress.

Conclusions: These results emphasize that carotenoids and BRs enhance cold resistance in pepper by enhancing antioxidant enzyme activities, scavenging reactive oxygen species (ROS) and transcriptional responses. This study provides new insights into the interactions between BR signaling and carotenoid metabolism under low-temperature stress and offers a potential strategy for improving low-temperature tolerance in crops.