The Breakthrough at Peking University School of Life Sciences

A team from Peking University's School of Life Sciences has unveiled a groundbreaking discovery in plant biology: a novel gene regulatory network (GRN) in strawberries that sustains circadian rhythms even under challenging low-temperature conditions. This finding, detailed in a recent high-impact publication, reveals how strawberries maintain essential biological timing mechanisms during postharvest refrigeration, a process that disrupts the standard plant circadian clock. For researchers and students in China's thriving higher education landscape, this represents not just a scientific milestone but a testament to PKU's leadership in life sciences research.

Circadian clocks, the internal biological timers that synchronize plant processes with day-night cycles, are crucial for growth, flowering, and stress responses. In most plants, cold temperatures like those in refrigerated storage cause these clocks to become arrhythmic, leading to accelerated deterioration. However, strawberries exhibit resilience through this alternative GRN, opening new avenues for genetic engineering and agricultural innovation.

The PKU team employed advanced genomic techniques, including RNA sequencing under controlled cold conditions and heterologous reconstitution in model organisms, to map this network. Their work highlights how specific transcription factors and feedback loops bypass the canonical clock, ensuring rhythmic gene expression for metabolism and quality preservation.

Understanding Circadian Clocks in Plants

To appreciate the significance, it's essential to grasp what a circadian clock entails in plants. The circadian clock is an endogenous oscillator with a roughly 24-hour period, regulating over 30% of the transcriptome. Core components include genes like CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB EXPRESSION 1 (TOC1), forming interlocking feedback loops.

In strawberries (Fragaria × ananassa), an octoploid species vital to global agriculture, these clocks influence fruit development, ripening, and response to environmental stresses. China, the world's largest strawberry producer with over 3.4 million tons annually—projected to reach 3.9 million by year-end—relies heavily on such research to enhance yield and shelf life.

PKU's Methodological Innovation

Led by prominent faculty in PKU's School of Life Sciences, the research integrated multi-omics approaches. Researchers profiled transcriptomes from strawberry fruits stored at 4°C, identifying persistent oscillations in key metabolic genes despite canonical clock disruption. Computational modeling reconstructed the GRN, pinpointing novel regulators such as strawberry-specific TCP transcription factors and sugar sensors.

Validation involved reconstituting the network in yeast and Arabidopsis, where it restored rhythms under cold stress. This heterologous system confirmed the GRN's autonomy, a step-by-step process: (1) Identify oscillating modules via time-series RNA-seq; (2) Infer regulatory interactions using machine learning; (3) Test in synthetic biology chassis; (4) Analyze functional outputs like hormone levels and enzyme activity.

PKU's state-of-the-art facilities, including the Plant Molecular Biology Lab, enabled this precision, underscoring the university's investment in cutting-edge infrastructure for life sciences students and postdocs.

Key Components of the Strawberry-Specific GRN

The novel GRN centers on a feed-forward loop involving FvTCP4, a TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) family member, and FvSWEET15, a sugar transporter. FvTCP4 activates evening-phased genes, while FvSWEET15 provides metabolic feedback, mimicking TOC1-LHY dynamics but temperature-insensitive.

• FvTCP4 binds promoter regions of 150+ clock-output genes, promoting anthocyanin accumulation for antioxidant protection.
• FvSWEET15 modulates sucrose levels, stabilizing repressor complexes under cold.
• Auxiliary modules include ERF transcription factors linking ethylene signaling to rhythm persistence.

This architecture explains why refrigerated strawberries retain firmness and flavor longer than expected, with experiments showing 20-30% extended shelf life.

Photo by Pedro Miguel Aires on Unsplash

Agricultural Implications for China's Strawberry Industry

China's strawberry sector, centered in Shandong and Liaoning provinces, faces postharvest losses of up to 25% due to spoilage. This discovery promises targeted breeding for cold-resilient varieties, potentially saving billions in economic value. For instance, integrating the GRN via CRISPR-Cas9 could yield cultivars with enhanced refrigeration tolerance.

Collaborations between PKU and the Chinese Academy of Agricultural Sciences are already underway, testing edited lines in field trials. Students in PKU's agronomy programs contribute through internships, bridging academia and industry.

FAO data underscores China's dominance, emphasizing the national stakes.

Broader Impacts on Plant Stress Biology

Beyond strawberries, the GRN model applies to other cold-stored crops like apples and grapes. It challenges the paradigm of universal clock fragility, suggesting species-specific backups evolved for perennial fruits. PKU researchers propose evolutionary conservation, with homologs in Rosaceae family.

In higher education, this fuels curricula in synthetic biology and chronobiology at Chinese universities, attracting top talent. PKU's graduate programs report increased applications in plant sciences post-publication.

PKU School of Life Sciences: A Hub for Excellence

Peking University's School of Life Sciences, established in 1920, boasts over 100 faculty specializing in molecular biology and genetics. Recent rankings place PKU among Asia's top 5 for life sciences, with breakthroughs in CRISPR plants and microbiome engineering.

The strawberry project exemplifies interdisciplinary training: undergrads handle phenotyping, master's students bioinformatics, PhDs lead reconstitution. Funding from NSFC and 863 Program supports 50+ labs, fostering China's next generation of biologists.

International partnerships, like with Max Planck Institute, enhance global visibility, positioning PKU as a leader in plant chronobiology.

Challenges and Future Directions

While promising, translating the GRN to commercial varieties requires overcoming polyploidy hurdles in strawberries. PKU plans speed-breeding platforms and AI-optimized networks for multi-stress resilience.

• Short-term: Validate in elite cultivars like 'Zhangji'.
• Medium-term: Field trials for export standards.
• Long-term: Extend to climate-adaptive clocks amid warming trends.

Stakeholders, including the Ministry of Agriculture, praise PKU's role in food security.

Photo by Miles Peacock on Unsplash

Perspectives from Chinese Academia

Experts at Tsinghua and CAS commend PKU's rigor, noting synergies with national initiatives like the 14th Five-Year Plan for biotech. Prof. Li Wei from PKU states, 'This GRN redefines plant clock resilience, vital for sustainable horticulture.'

For aspiring researchers, PKU offers scholarships and labs, detailed at their official site.

Conclusion: Elevating China's Higher Education in Biology

This discovery cements PKU's stature, inspiring universities nationwide. As China advances in precision agriculture, such innovations ensure leadership, benefiting students, faculty, and farmers alike.