Figure 1.

Function and regulation of cell‐wall invertase (Cw‐Inv) in plant–pathogen interactions (exemplified for fungal/bacterial leaf pathogens). Cw‐Inv cleaves sucrose (Suc), the major transport sugar, yielding glucose (Glc) and fructose (Frc). Pathogen challenge leads to an induction of Cw‐Inv expression or de‐repression of Cw‐Inv activity, mediated by the down‐regulation of proteinaceous Cw‐Inv inhibitors, resulting in enhanced sucrose cleavage. After uptake, hexoses are further metabolized to support respiration or the synthesis of secondary metabolites, notably the formation of callose or phenolic compounds. In addition, sucrose and hexoses act as signalling molecules. Therefore, Cw‐Inv locates at an integration point of hormonal, sugar, defence and diurnal/circadian regulation. The latter is a newly emerging aspect of Cw‐Inv regulation and could be crucial to the coordination of diurnal growth patterns and defence reactions. Moreover, Cw‐Inv is a target of pathogen effectors, underlining the importance of Cw‐Inv in the defence response. Black boxes represent sugar transporters. Dotted arrows depict metabolic reactions, broken arrows sugar transport and full arrows signalling interactions. PAMP, pathogen‐associated molecular pattern; ROS, reactive oxygen species.