Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - CHEMCOMRHIZO (Chemical communication in the rhizosphere of plants)

Teaser

In CHEMCOMRHIZO we study the use by plants of metabolites to communicate with other organisms in their rhizosphere. We are looking at biosynthesis and perception of rhizosphere signaling molecules. An exciting example of rhizosphere signalling molecules are the strigolactones...

Summary

In CHEMCOMRHIZO we study the use by plants of metabolites to communicate with other organisms in their rhizosphere. We are looking at biosynthesis and perception of rhizosphere signaling molecules. An exciting example of rhizosphere signalling molecules are the strigolactones. These are used by the friends of plants, the arbuscular mycorrhizal fungi, for host detection but also by their enemies, root parasitic plants. Furthermore, they have an endogenous signalling function, as a plant hormone that regulates shoot branching and root architecture. I postulated that this dual positive and negative signalling role of the strigolactones is the result of a paradigm: enemies of plants recruit molecules that are essential to the plant as cues. This paradigm has two important implications: 1) other plant-produced signalling molecules known to be abused by plant enemies likely have another, beneficial essential function in plants and 2) the involvement of multiple, positive and negative, biological functions exerts a selective pressure on these signalling molecules that results in the evolution of diversity in structure and biological specificity. For the strigolactones we are investigating implication 2): what is the biological relevance of the large structural diversity in the strigolactones. For implication 1) we are studying other rhizosphere signaling molecules that are abused by plant enemies such as nematodes. Together, the work should shed light on the significance of structural diversity in signalling molecules and the co-evolution of perception and could result in the discovery of a new class of signalling molecules in plants. It may also provide the basis for biotechnological and agronomical applications to optimise colonisation by AM fungi and plant development, and control parasitation by root parasitic plants and nematodes.

Work performed

In the first half of CHEMCOMRHIZO the PI moved from Wageningen University to the University of Amsterdam to establish a new group there, the Plant Hormone Biology group. After setting up the new lab, purchasing a new ultra-sensitive mass spectrometer and hiring the people on the project we set up a method called aeroponics to be able to collect root exudates of plants in high amounts and an analytical method for the detection of the rhizospohere signaling molecules that we investigate, such as the strigolactones. With these analytical methods we can support the molecular biological work that we do: identifying genes involved in the biosynthesis of rhizosphere signaling molecules. We have identified a large number of candidate genes using a number of different approaches such as gene co-expression analysis. And are now testing these candidate genes also through a variety of approaches such as through transient expression and with mutants in which the genes are knocked out. This has resulted in the identification of a number of strigolactone biosynthetic genes and regulators. We are also studying the perception of the rhizosphere signals by parasitic weeds and other organisms. In the first phase we have focused on receptors in nematodes and have used protein modelling to identify candidate receptors that we are now characterizing. Finally we are studying how plants use strigolactones and other compounds to attract beneficial micro-organisms to their roots. These micro-organisms can help the plant to withstand stressful conditions and we are showing that strigolactones play a role in this microbe recruitment by plants.

Final results

We anticipate to be able to fully elucidate the strigolactone biosynthetic pathways of tomato and maize as well as the pathways for the production of other important rhizosphere signaling molecules. With this knowledge we will be able to manipulate these pathways and show what the relevance is of all the different molecules secreted by plants into the soil. We eill also know how the enemies of plants are able to perceive these signaling molecules and with that knowledge will be able to optimize plants to not attract enemies (but to do attract their friends) and to develop agrochemicals that can be used to control these enemies. At the same time we are looking at the attraction of friends, such as beneficial microbes, and we anticipate to better understand how important plant signaling molecules are in this process.