Transcriptional and physiological analyses reveal the association of ROS metabolism with cold tolerance in tea plant

Tea plants are sensitive to cold stress and exhibit a high degree of genetic variability for cold tolerance. To understand the networks controlling cold tolerance in tea plants, transcriptome analyses were performed for non-acclimated (NA) and cold-acclimated (CA) conditions using one cold-resistant cultivar and two cold-susceptible cultivars. The comparison analysis found that the candidate regulators, including those involved in the oxidative stress response pathway, genes encoding protein kinases such as MPKs and CIPKs and transcription factors such as WRKYs and MYBs, contributed to the different cold tolerances of the three cultivars. The positive regulatory mechanism of OST1-ICE1 and the negative regulatory mechanism of MPK3-ICE1 were increased and decreased in the cold-resistant cultivar under CA, respectively. Compared with the cold-resistant cultivar, the cold-susceptible cultivars exhibited a higher ROS content along with lower SOD activity in the two-year repeated tests and subsequently experienced more severe leaf damage. The expression levels of ROS production and scavenging genes were higher and lower, respectively, in the two cold-susceptible cultivars under CA. Together, our results indicate that OST1 and MPK3 play vital roles in tea plant cold tolerance regulation, and the activation of ROS-scavenging genes is a primary strategy for tea plants to cope with cold stress during the winter season.