To stay healthy, plants balance the energy they put into growth with the amount they use to defend themselves from harmful bacteria. Although the mechanisms behind this balance are a mystery, North American scientists may have found an answer.
The team from Princeton University, in the United States, showed that some types of soil bacteria can influence the growth balance and defense of a plant.
According to , these bacteria produce a difficult capable of decreasing a plant’s immune activity and allowing its roots to grow longer than they would otherwise.
To look for these immune-balancing bacteria, the team looked at plants that were engineered to have large immune responses to a protein that makes up the threadlike appendages, called flagella.
The protein, called flagelinais a potent trigger of immune responses in plant and even human hosts.
In the laboratory, scientists cultivated Arabidopsis — a small plant from the mustard family that is widely used in scientific research — from a specific line that was engineered to produce high levels of flagellin-sensitive immune receptor in its roots.
When grown on plates that contained the piece of flagellin that activates the receptor, the roots proved to be quite shortas its energy was directed towards immunity instead of boosting growth.
The experiment involved the cultivation on plates with flagellin and 165 different bacterial species isolated from the roots of Arabidopsis. About 41% of this last sample suppressed the growth response by reducing plant immunity and allow your roots to grow.
One of the bacterial species that allowed roots to grow was Dyella japonica, a species whose previous work has already demonstrated that immunomodulatory activity depended on a bacterial secretion system — a complex of proteins that can move substances out of bacterial cells and into the environment, including within plant cells or in the spaces between them.
Further analysis of this species ended up revealing a gene that encodes a secreted enzyme – called subtilase – with the ability to cut flagellin into small pieces and prevent it from activating the immune response.
After using different genetic and biochemical methods, the team was able to demonstrate that the subtilase enzyme is indeed capable of degrading the specific segment of flagellin that triggers the immune response. Degradation is sufficient to contain the immune response and allow plants to grow.
The was published in Cell Reports.
