a, SWEETs (red) localized in the phloem parenchyma (a cell type of the plant vasculature), export sucrose produced by photosynthesis into the cell wall, from where it is loaded actively, with the help of the transporter SUT1 and energized by H+-ATPases into the actual conduits, the sieve element companion cell complex for translocation to seeds. Photosynthesis mainly occurs in the palisade parenchyma. b, The role of SWEETs as the ‘Achilles’ heel’ (susceptibility factors) of host plants during pathogen infection. SWEETs are induced directly as a consequence of the injection of transcriptional-activator-like effectors from pathogens via type III secretion systems into the infected plant cell, leading to release of sugars as a critical source of nutrition for the pathogens.