Sugar conundrum in plant-pathogen interactions: roles of invertase and sugar transporters depend on pathosystems

Analyses of diverse plant species and pathogens indicate that the specific roles of invertases and sugar transporters in plant-pathogen interactions depend on the lifestyle and infection strategies of pathogens. It has been increasingly recognized that CWIN (cell wall invertase) and sugar transporters including STP (sugar transport protein) and SWEET (sugar will eventually be exported transporters) play important roles in plant-pathogen interactions. However, the information available in the literature comes from diverse systems and often yields contradictory findings and conclusions. To solve this puzzle, we provide here a comprehensive assessment of the topic. Our analyses revealed that the regulation of plant-microbe interactions by CWIN, SWEET, and STP is conditioned by the specific pathosystems involved. The roles of CWINs in plant resistance are largely determined by the lifestyle of pathogens (biotrophs versus necrotrophs or hemibiotrophs), possibly through CWIN-mediated salicylic acid or jasmonic acid signaling and programmed cell death pathways. The up-regulation of SWEETs and STPs may enhance or reduce plant resistance, depending on the cellular sites from which pathogens acquire sugars from the host cells. Finally, plants employ unique mechanisms to defend against viral infection, in part through a sugar-based regulation of plasmodesmatal development or aperture. Our appraisal further calls for attention to be paid to the involvement of microbial sugar metabolism and transport in plant-pathogen interactions, which is an integrated but overlooked component of such interactions.

Automated summary

Analyses of plant species and pathogens show that specific roles of invertases and sugar transporters in plant-pathogen interactions depend on the lifestyle and infection strategies of pathogens. Cell wall invertase (CWIN), sugar transport proteins (STP), and sugar will eventually be exported transporters (SWEET) play important roles in plant-pathogen interactions. However, there are contradictory findings and conclusions in the literature. Further studies on microbial sugar metabolism and transport in plant-pathogen interactions are needed.