"This work is important because it connects the different puzzle pieces of systemic immunity, so we can begin to see the connections between the pieces and the framework of an overall picture," said Aardra Kachroo.

She and her husband, Pradeep Kachroo, are researchers in the UK Department of Plant Pathology and study plant responses to microbial pathogens. Their focus has been focused on resistance pathways that, when triggered, can fend off oomycete, fungal, bacterial and viral pathogens.  The report that some of these pathways exist in all organisms.

Researchers in their labs found that cell-signaling molecules nitric oxide and reactive oxygen species are required to start systemic acquired resistance. This form of resistance protects plants against secondary infections. When genetic mutations in plants prevent the production of either nitric oxide or reactive oxygen species, the plant cannot produce systemic acquired resistance.

"Nitric oxide and reactive oxygen species are already well known to be associated with many human disorders,” said Pradeep Kachroo. “Although they have long been identified as signaling molecules in plants as well, it is exciting to know they are also key regulators of systemic immunity. This is the closest system in plants to the human circulatory immune system."

Medical researchers have linked an imbalance of nitric oxide and reactive oxygen species in the human body to incurable age-related, neurodegenerative diseases like Alzheimer’s and Parkinson’s, as well as many types of cancers.

“Some levels of ROS (reactive oxygen species) are actually needed for human well-being and are in fact beneficial,” said Pradeep Kachroo. “This is the same for plants. Too little or too much of ROS/nitric oxide can impair many processes including plant immunity."

Researchers involved with the finding are Caixia Wang, Mohamed El-Shetehy, M.B. Shine, Keshun Yu, all current or former members of one of the Kachroo labs, and two collaborators, Duroy Navarre and David Wendehenne.

The Kachroos previously discovered the metabolite glycerol-3-phosphate as an inducer of systemic immunity in plants and demonstrated its relationship to another defense activator, azelaic acid.

Their most recent findings, published in Cell Reports, show a connection between nitric oxide and reactive oxygen species and those previously identified immune activators. 

Source: Report by Katie Pratt, University of Kentucky