Research Reveals Transcriptional Mechanism Behind Salt Tolerance in Watermelon

High soil salinity disrupts water absorption, ion balance, and photosynthesis in plants, leading to growth inhibition and yield loss. In many crops, excessive sodium ions compete with essential potassium, causing osmotic stress and oxidative damage. To survive these harsh conditions, plants rely on transcription factors such as WRKYs and stress-protective proteins like LEAs, which help maintain cellular stability. However, the specific molecular mechanisms by which WRKY and LEA proteins coordinate salt tolerance in watermelon remain unclear. Based on these challenges, it is necessary to explore how WRKY transcription factors and LEA proteins jointly regulate watermelon's adaptation to saline environments.

Researchers from the State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, together with collaborators from Ningxia Academy of Agriculture and Forestry Sciences and Northeast Agricultural University, have identified a transcriptional mechanism that enhances salt tolerance in watermelon. The study (DOI: 10.1093/hr/uhae320), published in Horticulture Research on 1 March 2025, reveals that ClWRKY61 interacts directly with ClLEA55 to regulate stress-responsive genes. Using CRISPR/Cas9 knockout and overexpression analyses, the team demonstrated that this interaction significantly improves watermelon's physiological performance under high-salt conditions.

The scientists discovered that ClWRKY61, a gene encoding a WRKY transcription factor, is highly expressed in watermelon roots and leaves when exposed to 300 mM NaCl. Gene editing experiments confirmed its positive role in salt tolerance: knockout plants exhibited severe wilting, higher membrane damage, and lower superoxide dismutase (SOD) activity, while overexpression lines maintained healthier leaves and lower salt injury indices.

Through yeast two-hybrid, GST pull-down, luciferase complementation, and bimolecular fluorescence assays, the ClWRKY61 protein was shown to physically interact with the ClLEA55 protein, a late embryogenesis abundant (LEA) protein known for its role in cellular protection. Mutants lacking ClLEA55 displayed similar salt-sensitive phenotypes, confirming its synergistic function.

RNA sequencing further revealed 554 differentially expressed genes in the ClWRKY61 knockout lines, including many with WRKY-binding W-box motifs. These genes are involved in hormone signaling, antioxidant metabolism, and osmotic regulation, such as those encoding phytoene synthase, MYB and ERF transcription factors, sucrose synthase, glutathione reductase, and calcium-dependent protein kinases. Together, these results illustrate how the ClWRKY61–ClLEA55 regulatory module coordinates transcriptional and metabolic responses to salinity stress.

Our findings reveal a direct link between transcriptional regulation and stress-protective proteins in watermelon. By forming a complex with the ClLEA55 protein, the transcription factor encoded by ClWRKY61 activates a network of genes that mitigate oxidative damage and maintain ion homeostasis. This not only deepens our understanding of WRKY family function under stress but also provides promising molecular targets for engineering watermelon and other cucurbit crops with improved tolerance to salinity."

Prof. Xian Zhang, corresponding author of the study

This research lays the groundwork for developing salt-tolerant watermelon cultivars through molecular breeding and gene editing. The ClWRKY61–ClLEA55 module could serve as a valuable genetic marker or regulatory hub for improving stress resilience in crops grown in arid and saline regions. Since salinity affects more than 8% of global arable land, applying such molecular insights could enhance sustainable crop production and food security. Beyond watermelon, this study also provides a model for understanding transcription factor–protein interactions that safeguard other crops against environmental stress.