Abstract
Xylem vascular wilt pathogens cause devastating diseases in plants. Proliferation of these pathogens in the xylem causes massive disruption of water and mineral transport, resulting in severe wilting and death of the infected plants. Upon reaching the xylem vascular tissue, these pathogens multiply profusely, spreading vertically within the xylem sap, and horizontally between vessels and to the surrounding tissues. Plant resistance to these pathogens is very complex. One of the most effective defense responses in resistant plants is the formation of physico-chemical barriers in the xylem tissue. Vertical spread within the vessel lumen is restricted by structural barriers, namely, tyloses and gels. Horizontal spread to the apoplast and surrounding healthy vessels and tissues is prevented by vascular coating of the colonized vessels with lignin and suberin. Both vertical and horizontal barriers compartmentalize the pathogen at the infection site and contribute to their elimination. Induction of these defenses are tightly coordinated, both temporally and spatially, to avoid detrimental consequences such as cavitation and embolism. We discuss current knowledge on mechanisms underlying plant-inducible structural barriers against major xylem-colonizing pathogens. This knowledge may be applied to engineer metabolic pathways of vascular coating compounds in specific cells, to produce plants resistant towards xylem colonizers.
Highlights
The plant immune system has been shaped by hundreds of millions of years of interactions with microbial pathogens that are constantly trying to evade or overcome host plant defense reactions
If a pathogen manages to reach the xylem, this transport system becomes an excellent channel of inoculum dissemination throughout the plant.As a consequence, plants have evolved effective structural defense mechanisms to prevent vessel colonization or movement between vessels once vascular colonization has occurred (Beckman and Roberts, 1995) Timely formation of these physico-chemical vascular barriers early upon pathogen perception can lead to confinement of the vascular pathogen at the infected vessel, avoiding the spread of wilt diseases (Robb et al, 2007; Zaini et al, 2018; Planas-Marquès et al, 2019)
We summarize how inducible vascular structures compartmentalize the vascular wilt pathogens leading to resistance
Summary
The plant immune system has been shaped by hundreds of millions of years of interactions with microbial pathogens that are constantly trying to evade or overcome host plant defense reactions. If a pathogen manages to reach the xylem, this transport system becomes an excellent channel of inoculum dissemination throughout the plant.As a consequence, plants have evolved effective structural defense mechanisms to prevent vessel colonization or movement between vessels once vascular colonization has occurred (Beckman and Roberts, 1995) Timely formation of these physico-chemical vascular barriers early upon pathogen perception can lead to confinement of the vascular pathogen at the infected vessel, avoiding the spread of wilt diseases (Robb et al, 2007; Zaini et al, 2018; Planas-Marquès et al, 2019) Some of these structural reinforcements induced by pathogens were already reported in classic botanical studies in the 19th century (Zimmermann, 1979).
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