Sugar rush spurs plants to grow up

U. PENNSYLVANIA (US) — Like animals, plants go through several stages of development before they reach maturity, and new research clarifies sugar’s role in the process.

It has long been thought that some of the transitions between these stages are triggered by changes in the nutritional status of the plant.

Based on experiments with the plant Arabidopsis thaliana, a team of researchers have discovered the role of sugar in “vegetative phase change,” the transition from the juvenile form of a plant to the adult plant.


“It has been known for a long time that mineral nutrients and sugars can affect plant growth, but it has been unclear until now if they trigger developmental transitions,” says Scott Poethig, a biology professor at the University of Pennsylvania.

Published online in the journal eLife, the new work takes advantage of the fact that vegetative phase change is controlled by two genes that encode microRNAs, or miRNAs.

Arabidopsis has eight miR156 genes, but researchers confirmed that supplying plants with sugar reduces the expression of just two of these—miR156A and miR156C—while sugar deprivation increases their expression. Researchers found that removing leaves also leads to upregulation of both genes and delays the juvenile–to–adult transition.

Given that this effect can be partially reversed by providing the plant with sugar, it is likely that sugar produced in the leaves, or one of its metabolites, is the signal that triggers the juvenile–to–adult transition through the reduction of miR156 levels.

Consistent with this idea, Poethig and colleagues revealed that plants genetically engineered to be deficient in chlorophyll showed elevated levels of miR156 and a delayed transition to the adult form. In addition, a gene called HXK1, which encodes a glucose signaling protein, helps to keep plants in the juvenile form under conditions of low sugar availability.

HXK1 also contributes to the glucose-induced decrease in miR156 levels and does so, at least in part, by regulating the transcription of miR156A and miR156C genes into messenger RNA.

HXK1 is not solely responsible for the juvenile–to–adult transition, however, because plants that lack this protein are only slightly precocious in their transition to the adult form.

“Our results are significant,”  Poethig says, “because they demonstrate that nutrition is important for developmental maturation in plants—the switch from juvenile to adult development — just as it is in animals, including humans.”

The study was supported by the National Institutes of Health.

Source: University of Pennsylvania