Catch Me If You Can: How Xylella fastidiosa Thrives in the Xylem.

The outcome of infection can be seen as a race between the pathogen and the plant immune system. In this review, we use the case study of Xylella fastidiosa (Xf) and explain how the bacterium exploits its slow and fastidious growth to remain below detection thresholds, thereby delaying immune activation. Its self-limiting behavior in the sessile state provides a temporal window for transitioning into a more exploratory lifestyle, enabling systemic colonization of the host. As bacterial populations expand, vessel occlusion and immune overactivation at late stages occur, often propagating beyond directly infected tissues, leading to hydraulic collapse and drought-like symptoms. We highlight how Xf's adaptations to a nutrient-poor and rapid-flow environment contribute to its persistence. Furthermore, we discuss how resistant plant genotypes, possessing broader or more sensitive repertoires of immune receptors, can detect the pathogen earlier and restrict its systemic spread in the xylem. Understanding the dynamics of these "catch me if you can" strategies may guide novel approaches to reduce Xf survival and mitigate disease progression in susceptible crops while also providing broader insights into plant responses and the infection strategies of other xylem-inhabiting microbes.