A research team from Huazhong Agricultural University's (HZAU) National Key Laboratory of Agricultural Microbiology and Hubei Hongshan Laboratory has identified a novel mechanism that enables tomatoes to resist major bacterial and fungal pathogens.

The study, titled Differential Phosphorylation of Receptor Kinase SlLYK4 Mediates Immune Responses to Bacterial and Fungal Pathogens in Tomato, published in Science Advances, offers new insights into crop immunity and may contribute to the development of disease-resistant varieties.

Led by Professor Li Bo, the team discovered how the receptor kinase SlLYK4 in tomatoes detects pathogens and triggers immune responses. The researchers revealed that SlLYK4 recognizes extracellular polysaccharides from Ralstonia solanacearum, a bacterium responsible for bacterial wilt — a devastating soilborne disease affecting tomatoes, potatoes, and other solanaceous crops.

The study found that SlLYK4's function depends on site-specific phosphorylation, which activates distinct immune pathways. When SlLYK4 is knocked out, tomatoes show reduced immune responses and increased susceptibility to both bacterial wilt and Fusarium wilt caused by the fungus Fusarium oxysporum.

Working model of SlLYK4-mediated resistance to bacterial and fungal pathogens. [Photo/news.hzau.edu.cn]

SlLYK4 also forms a protein complex with related kinases SlLYK1 and SlLYK13. Mass spectrometry and site-directed mutagenesis revealed that phosphorylation at serine 634 is essential for bacterial polysaccharide-triggered immunity, while phosphorylation at serine 334 mediates responses to fungal chitin.

This discovery not only identifies the first known receptor complex in tomatoes for sensing R. solanacearum polysaccharides, but also explains how a single immune receptor can direct different defense responses. The findings provide valuable genetic resources for breeding disease-resistant crops.