[Chih-Hang Wu] The Defense of Tomato Roots: A Specialized NLR Gene Cluster Against Nematodes
POST:
The earliest NRC genes appeared about 125 million years ago. Later, around 17 to 21 million years ago, a new gene cluster emerged in the ancestors of tomato and other Solanum species. This cluster includes NRC6 and other genes that help defend against nematode infection, and is expressed only in the roots.
In the plant immune system, a key group of proteins known as NLRs (nucleotide-binding domain and leucine-rich repeat receptors) detect pathogen invasion and trigger defense responses. How NLRs function differently across plant organs has remained unclear. Recent research discovered that tomato possesses a cluster of NLR genes expressed almost exclusively in roots, including the nematode resistance genes Hero and MeR1, and the helper gene NRC6.
This root-specific gene cluster originated about 21 million years ago, evolving from ancient NRC network genes through duplication and diversification. Experiments show that these sensor NLRs require NRC6 to activate the plant’s characteristic hypersensitive cell death response, which blocks further nematode infection. In other words, NRC6 functions as a “switch,” essential for triggering immune activation in this system.
This finding reveals that plant immune networks can diversify according to organ-specific functions. Some NLR gene clusters appear to have evolved specialized roles to protect specific organs—such as roots—against distinct pathogens, while minimizing the risk of excessive immune activation that could harm the plant itself. This highlights the remarkable adaptability and evolutionary flexibility of the plant immune system.