# Physiological Responses and Transcriptome Analysis of Camellia reticulata Under Low-Temperature Stress

## TL;DR

This study explores how Camellia reticulata responds to cold stress through physiological changes and gene activity, offering insights for breeding cold-tolerant varieties.

## Contribution

The study identifies key physiological and transcriptomic responses to cold stress in Camellia reticulata, providing a basis for cold-tolerant breeding.

## Key findings

- Soluble protein content increased continuously, while soluble sugar content fluctuated under cold stress.
- Transcriptome analysis identified 10,816 differentially expressed genes, with key roles in metabolism and stress response pathways.
- Cold stress significantly affected glucose, lipid, and amino acid metabolism, as well as hormone signaling and redox systems.

## Abstract

Background: Camellia species are highly ornamental but sensitive to habitat temperature, making cross-border domestication challenging. Methods: In this study, physiological indicators and transcriptome data of Camellia reticulata ‘shizhitou’ were analyzed to identify key factors involved in the response to cold. Results: The findings provide a scientific basis for the conservation of Camellia germplasm resources and breeding of cold-tolerant varieties. Under prolonged low-temperature stress, significant changes were observed in the physiological indices of C. reticulata ‘shizhitou’. Among soluble substances, soluble protein content continuously increased, while soluble sugar content exhibited a fluctuation pattern of increase–decrease–increase. Under prolonged low-temperature stress, significant changes were observed in the physiological indexes of C. reticulata ‘shizhitou’, while soluble sugar content exhibited a fluctuation pattern of increase–decrease–increase. Overall, soluble sugar and soluble protein contents were significantly positively correlated. Chlorophyll content initially decreased and then increased, whereas peroxidase (POD) and catalase (CAT) activities fluctuated and were negatively correlated with chlorophyll content. Malondialdehyde (MDA) content showed an irregular fluctuation trend. A total of 56,424 unigenes were obtained by transcriptome sequencing, of which 39,278 were annotated, while 10,816 differentially expressed genes (DEGs) were identified, including 5748 up-regulated and 5068 down-regulated genes, with 143 DEGs commonly shared across conditions. Congclusions: Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that low-temperature stress significantly influenced glucose metabolism, lipid metabolism, and amino acid metabolism, and the core pathways of cold stress included zeatin synthesis, hormone signaling, and galactose metabolism. Both physiological responses and transcriptome-based enrichment of DEGs indicate that the redox system and metabolic pathways play crucial regulatory roles in C. reticulata under cold stress.