• EMS-induced Camellia japonica mutant line #79 shows enhanced cold tolerance via multi-pathway synergy and metabolic reallocation. • Integrative reprogramming at molecular, physiological, and morphological levels preserves line #79 integrity under cold stress. • Stable cold-tolerant Camellia line #79 and its key genes enable precision breeding of woody ornamentals. • The cold adaptation mechanism in Camellia informs research on cold-sensitive woody ornamentals. Limited cold tolerance severely restricts the cultivation and ornamental value of Camellia japonica . However, research on the creation of cold-tolerant mutants in perennial woody ornamentals remains scarce, and the underlying molecular mechanisms are largely unknown. To address this gap, we used a semi-lethal concentration (LC₅₀) of 0.8% ethyl methylsulfonate (EMS) to screen 80 candidate lines. Through start codon targeted polymorphism (SCoT) and conserved DNA-derived polymorphism (CDDP) markers combined with phenotypic evaluation (dense lateral roots, shortened internodes), line #79 was selected for in-depth study. Its cold tolerance mechanism was systematically investigated via transcriptomics, low-temperature stress treatments, and physiological assays. Transcriptomic analysis revealed coordinated activation of stress-responsive pathways, including phenylpropanoid biosynthesis, flavonoid biosynthesis, starch and sucrose metabolism, plant hormone signal transduction, MAPK signaling, and circadian rhythm. Under cold stress, line #79 exhibited significantly less leaf chlorosis and curling than the wild-type. Physiological validation showed that line #79 accumulated higher levels of lignin, sucrose, and fructose, exhibited elevated peroxidase (POD) and catalase (CAT) activities, and demonstrated enhanced reactive oxygen species (ROS) scavenging capacity. Collectively, a stable cold-tolerant EMS mutant line (#79) was obtained. Its enhanced cold tolerance relies on a multi‑mechanism synergistic network integrating structural reinforcement, osmotic regulation, and oxidative defense. This study addresses this problem by providing elite germplasm and molecular targets for cold tolerance breeding in Camellia , and offers a new strategy for stress resistance improvement in woody ornamental plants.
Yin et al. (Wed,) studied this question.