Comparative proteomics analysis of contrasting Camellia sinensis genotypes exposed to cold acclimation and freezing stress

Tea plants (Camellia sinensis) are highly sensitive to cold stress and exhibit significant genetic variability in cold tolerance. Although multiple studies have explored low-temperature response mechanisms, the physiological and proteomic basis underlying variation in cold tolerance among Camellia sinensis cultivars remain unclear. In this study, we conducted a comparative physiological and proteomic analysis of a cold-tolerant (SCZ) and a cold-sensitive (YH9) variety under cold acclimation and freezing stress. The cold-tolerant genotype SCZ exhibited greater cold tolerance than YH9, as evidenced by the accumulation of starch granules, less pronounced structural changes in chloroplasts, and a relatively higher Fv/Fm ratio. Using an iTRAQ-based proteomic approach, a total of 201, 261, 71, 70, 153 and 148 differentially abundant proteins (DAPs) were found in the comparisons of NA-CS vs. NA, CA vs. NA, and CA-CS vs. CA in SCZ and YH9, respectively. During cold acclimation, SCZ reduced light-induced damage through downregulation of photosynthesis-related proteins (Lhca, Lhcb, Psb, Psa, Pet, and ATPF) and ROS metabolic proteins (APX-2, GST-2/3/4/5/6, GRX-2), while upregulating the anthocyanin-related protein BZ1. In contrast, YH9 showed uncoordinated expression of ROS-scavenging enzymes, such as downregulation of GST-5 and PRX-2, alongside upregulation of SOD-2, GSR-1/2, GST-1, and GST-8. Notably, under freezing stress, cold-acclimated SCZ seedlings upregulated photosynthesis-related proteins (Lhca2, Lhcb2, PsbQa, PsaH, PsaN) and polyphenol metabolic pathway-related proteins (FLSc, ALDH), while downregulating ROS metabolism-related proteins (SOD-1, CAT-1/2/3, PRX-2). This response differred from that of non-acclimated SCZ seedlings, as well as both non-acclimated and acclimated YH9 seedlings under short-term freezing stress. Protein-protein interaction network analysis identified PSAN, LHCB5, PSAF, LHCB4.1, and others as potential hub proteins, suggesting their central regulatory roles in cold tolerance. However, their biological functions require further validation. Our findings reveal distinct proteomic and physiological strategies between two tea cultivars with contrasting cold tolerance, providing candidate targets and a theoretical foundation for future breeding efforts.