Plant immune system is capable of detecting conserved bacterial molecules which act as a tell-tale for the presence of invading bacteria. When this happens, immune responses get activated to prevent the development of a disease. The best studied case is that of flagellin, the protein that forms the bacterial flagellum.

To detect different parts of bacterial flagellin and activate the plant immune system upon bacterial invasion, plants have evolved immune receptors. They can easily detect the flagellum as indication of bacterial presence as most bacterial pathogens need it to move and cause disease, and a potential loss of the flagellum to evade this recognition would render a bacterium motionless and non-infecting.

Ralstonia solanacearum is the causal agent of the bacterial wilt disease, which affects important crops such as potato, tomato, tobacco, and banana. Recently, Dr. Alberto Macho at the Shanghai Center for Plant Stress Biology, Chinese Academy of Sciences uncovered that R. solanacearum has evolved to modify its flagellum to make it undetectable by immune receptors in plants from the Solanaceae family, which comprise economically important crops. The study was published in Plant Biotechnology Journal. 

This study also revealed that several species from this same family (for example, tomato and tobacco) can perceive another molecule present in R. solanacearum, named Cold-Shock Protein (CSP), which is produced in bacteria under stressful conditions. Specific plants, such as tomato and tobacco, have in turn developed an immune receptor, named CORE, which perceives bacterial CSP and activates the plant immune system. However, other plant species, lacking CORE, are not able to detect bacterial CSP.

Notably, treatment with purified CSP from R. solanacearum increases resistance to bacterial wilt disease in tomato plants. Moreover, transgenic expression of the CORE receptor in the model plant Arabidopsis thaliana, which naturally lacks it, renders this plant more resistant to infection by R. solanacearum.

This work uncovered the first molecule from Ralstonia perceived by Solanaceae plants and the corresponding receptor, and suggested that the inter-family transfer of this receptor to non-responsive plant species could increase the resistance of economically relevant crop species against bacterial wilt disease. Importantly, non-Solanaceae plants and several agronomically important solanaceous plants cannot perceive CSP.

Transgenic approaches will allow for the transfer of the CORE receptor to such plant species, generating an additional layer of resistance against R. solanacearum, and will contribute to current efforts to fight against bacterial wilt in crop plants.