Plants produce sugars by the process of photosynthesis; but how those sugars are exported from the cells that make them to nourish other parts of the plant has remained a mystery for many years.
Now it's been solved, and the discovery of a family of sugar-secreting pores could hold the key to new ways to combat plant-attacking pests and even remedy certain sugar-related metabolic problems in humans.
Writing in Nature, Carnegie Institution for Science-based researcher Wolf Frommer and his colleagues described how they have identified a clutch of genes, dubbed SWEETS, that allow sugars to exit cells. They made the breakthrough by initially screening the genome of the experimental plant arabidopsis for potential genes that looked like they might be linked to sugar metabolism.
Ingeniously, they then expressed, together with a fluorescent marker that glowed in the presence of glucose, the candidate genes in cultured human cells called HEKs. Critically, these cells pick up sugars quite poorly, which enabled the researchers to pinpoint when the cells were picking up sugars more efficiently, indicating that a sugar-transporting pore must be operating. And by looking where in the cell the sugars were accumulating, they were able to confirm that the genes they had identified were encoding pores that could transport sugars out of cells.
A scan of both plant and animal genomes confirms that both groups of organisms have their own versions of these genes and there are at least 21 of them in rice and one in humans. Studying how they work and how plants and other organisms use them to translocate sugars will provide valuable insights into a previously poorly-understood aspect of plant and animal physiology. But even more exciting is the finding that these pores also hold the key to making plants vulnerable to bacterial and fungal attack.
These pathogens appear to produce signals that target and activate these pores, forcing cells to secrete sugars and thus feed their attackers. Suppressing the pore function renders a plant immune to diseases like blight and powdery mildew, suggesting that such a technique could be used to provide a whole new way to protect plants from microbial attack.