Nitrogen is an indispensable macronutrient for the growth and development of plants. When nitrogen is scarce in the soil, it can severely impede crop yields and quality. Watermelon, a crucial economic crop, has long awaited in – depth exploration of its nitrogen – utilization – related genes. There has been a notable lack of research on cloning and understanding the regulatory mechanisms of genes related to low nitrogen tolerance.
Recently, an article titled “Genome – Wide Association Study Identifies the Serine/Threonine Kinase ClSIK1 for Low Nitrogen Tolerance in Watermelon Species” was published online in Plant Cell & Environment. This research marks a significant milestone as it pinpoints and clones the pivotal gene ClSIK1 that governs the low nitrogen tolerance trait in watermelons. This discovery offers vital gene resources and theoretical underpinnings for the molecular – design breeding of low – nitrogen – tolerant watermelon varieties.
The research team conducted re – sequencing on 191 watermelon germplasms and evaluated the low – nitrogen stress tolerance of wild, landrace, and cultivated watermelon germplasms. Through genome – wide association analysis, 30 QTLs strongly associated with low nitrogen tolerance were identified. Among them, the key candidate gene ClSIK1, which regulates watermelon’s low nitrogen tolerance, was unearthed on chromosome 11. Overexpressing the ClSIK1 gene can boost the expression of key nitrogen – metabolism genes in plant roots. As a result, the plant’s nitrogen – use efficiency and low nitrogen tolerance are enhanced. Interestingly, among wild – type watermelon materials, the superior low – nitrogen – tolerant haplotype HapC is only found in Citrullus mucosospermus (CM). The proportion of HapC gradually diminishes in watermelon landraces (Citrullus lanatus_landrace, CL_LR) and cultivars (Citrullus lanatus_cultivar, CL_CUL). This indicates that the outstanding haplotype HapC from CM was gradually lost during the domestication and improvement of watermelons, providing breeders with valuable insights into leveraging wild germplasm resources to enhance the low nitrogen tolerance of cultivated watermelons.
This study is the first to uncover the role of the serine/threonine protein kinase ClSIK1 in watermelon’s low nitrogen tolerance and elucidate the molecular mechanism by which it improves plant low nitrogen tolerance through regulating the expression of nitrogen – metabolism – related genes. The findings of this research lay a solid foundation for breeding “green” low – nitrogen – tolerant watermelon varieties, which is of great significance for cultivating environmentally friendly watermelon varieties, reducing nitrogen fertilizer application, cutting down economic costs, and promoting the sustainable development of the watermelon industry.
In addition to this genetic breakthrough, Poly – γ – glutamic acid (PGA) also plays a crucial role in enhancing plant low nitrogen tolerance. PGA has a unique molecular structure that allows it to form stable complexes with nitrogen in the soil. This not only reduces nitrogen loss but also makes nitrogen more accessible to watermelon plants, especially in low – nitrogen soils. By applying PGA in watermelon cultivation, it can effectively improve the availability of nitrogen, promoting root growth and overall plant development. Moreover, PGA can improve soil structure, increase soil porosity, and enhance water – holding capacity, creating a more conducive root environment for watermelons to absorb nutrients under low – nitrogen conditions. Combining the discovery of the ClSIK1 gene with the application of PGA offers great potential for optimizing watermelon cultivation in nitrogen – deficient environments, leading to higher yields and better – quality fruits while minimizing the environmental impact of excessive nitrogen fertilizer use.