Heed my warning
NAD molecules warn plants of invading bacteria by binding to a receptor protein called LecRK-I.8.
Plants and animals are generally healthy, despite being surrounded by many different microbes that have the potential to infect them and cause disease. This is because plants and animals are able to sense infections and promptly activate immune responses against them. A molecule known as NAD is involved in many processes inside healthy cells, but it can also act as a warning signal of infection. When an invading microbe damages a host cell, NAD leaks out of the damaged cell. Neighboring healthy cells sense this NAD and activate immune responses.
It is thought that specific receptor proteins on the surface of animal and plant cells are responsible for detecting NAD that has leaked out of damaged cells. However, the identities of these receptors were not known. Chenggang Wang, Mingji Zhou and colleagues used genetics and biochemical techniques to investigate how cells in a plant known as Arabidopsis detect NAD.
The experiments reveal that a receptor protein called LecRK-I.8 can bind NAD via a section of the receptor known as the lectin domain. Arabidopsis plants with mutant forms of LecRK-I.8 are less able to activate immune responses when exposed to NAD compared to normal plants. Furthermore, the mutant plants are less able to defend themselves against Pseudomonas syringae, a bacterium that can infect many different plants. On the other hand, plants with higher levels of LecRK-I.8 than normal produce stronger immune responses to NAD.
The findings of Wang, Zhou and colleagues identify the first receptor on the surface of plant cells that can detect NAD. The next challenge is to find out if humans and other animals also use similar proteins to detect NAD during infections. In agriculture, bacterial infections can lead to major losses of crops. Therefore, these findings may help researchers to develop crop varieties that are more resistant to these infections.
To find out more
Read the eLife research paper on which this eLife digest is based: “A lectin receptor kinase as a potential sensor for extracellular nicotinamide adenine dinucleotide in Arabidopsis thaliana” (Jul 19, 2017).
