Nonheading Chinese cabbage (NHCC) is an important Brassica vegetable valued for its short growth cycle, high yield, and nutritional quality. However, it grows best under mild temperatures and is vulnerable to sustained heat, which can impair photosynthesis, accelerate leaf senescence, disturb antioxidant balance, and reduce marketable quality. Plant responses to heat are also shaped by the timing and duration of exposure, but these factors have often been studied separately from circadian regulation in Brassica crops. Based on these challenges, deeper research is needed into how heat duration and circadian rhythm jointly regulate thermotolerance in NHCC.
The study was conducted by researchers from Nanjing Agricultural University, Jiangsu Vocational College of Agriculture and Forestry, the Sanya Institute of Nanjing Agricultural University, and the Shanghai Academy of Agricultural Sciences. Published (DOI: 10.1093/hr/uhag033) on February 9, 2026, in Horticulture Research, the article used time-resolved RNA sequencing (RNA-seq), weighted gene coexpression network analysis (WGCNA), transgenic plants, and molecular assays to define how BcCCA1 controls heat tolerance through BcHSFA2.
The researchers exposed NHCC seedlings to 43°C and collected leaf samples across multiple time points to compare early and prolonged heat responses. RNA-seq identified 13,863 differentially expressed genes (DEGs), including 3,531 genes specific to Day 1, 3,060 genes specific to Day 4, and 7,272 genes shared across both stages. Early responses were dominated by stimulus perception, signal transduction, calcium-related pathways, glutathione metabolism, and autophagy, indicating a rapid alarm-and-repair strategy. By Day 4, the response shifted toward antioxidant metabolism, nitrogen remobilization, reduced photosynthetic capacity, and leaf senescence. WGCNA further connected circadian regulation with heat-responsive gene modules. Molecular assays showed that the BcCCA1 protein binds directly to the promoter of BcHSFA2 and represses its transcription. Plants overexpressing BcHSFA2 showed less wilting, higher proline accumulation, and stronger catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activities, while BcCCA1 knockout mutants displayed enhanced heat tolerance.
The authors said the work reveals a direct molecular bridge between the plant body clock and heat-defense activation. They said the BcCCA1–BcHSFA2 module helps explain why heat tolerance depends not only on temperature intensity, but also on timing and exposure duration. Under heat, reduced BcCCA1 expression releases its repression of BcHSFA2, allowing stronger protective responses to begin. This regulatory switch, they said, provides a clearer view of how NHCC balances normal circadian control with emergency survival under high-temperature conditions.
These findings may support the development of heat-resilient leafy vegetables as climate warming intensifies. Because BcCCA1 acts as a negative regulator of thermotolerance, reducing or fine-tuning its activity could help crops withstand heat waves. Enhancing BcHSFA2-mediated responses may also strengthen antioxidant defenses and reduce heat-induced wilting. More broadly, the study suggests that breeding programs should look beyond individual stress-response genes and consider circadian control systems that determine when protective genes are activated. This clock-based perspective could enable more precise molecular breeding for stable vegetable production under future climate conditions.
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References
DOI
10.1093/hr/uhag033
Original Source URL
https://doi.org/10.1093/hr/uhag033
Funding information
This work was supported by the Shanghai Agricultural Science and Technology Innovation Program (Grant No. K2023015) and Project supported by the Education Department of Hainan Province, project number: Hnjg2025ZD-98.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.