Atypical immunity induced by extracellular water in plants

Microbial pathogens necessitate nutrients and water to thrive and multiply. These pathogens employ virulence factors to acquire resources, with these factors varying in form but sharing a common purpose. A common virulence tactic used by numerous pathogens to cause disease is inducing a water-rich extracellular space, or apoplast, in their host. This water-soaked lesion is prevalent among pathogens.

The question arose: how do plants respond to pathogen-induced extracellular water? The study found that inducing a water-soaked apoplast triggers an unusual transcriptional response but ultimately results in a functional immune response. This response effectively curtails pathogen growth, similar to the canonical pattern-triggered immunity seen in plants.

Investigating the underlying mechanisms, the research identified the immune phytohormone salicylic acid (SA) as crucial in mediating apoplastic water-induced immunity (AWII).

The findings imply that plants engage in an immune-priming program in response to apoplastic water accumulation. This suggests that the pathogenic niches formed during infection might be perceived as danger signals by the plant.