Back To The Roots

Chemical communication in the rhizosphere

It is generally known that plants are bound to their location by the roots. Despite this sessile lifestyle the plants are not completely defenseless against adverse environmental conditions. Rather they have mechanisms that help them cope with drought, nutrient deficiency, pathogens and other stress factors. To a large extent they do this with their roots. Plants are able to adapt and modulate the vicinity of their roots (rhizosphere) according to their individual needs. How they do this is the subject of a major new research initiative as part of the Pact for Research and Innovation at the IPB.

Abb. 1 The immediate environment of the root is called rhizosphere. It can be modulated by the plant in adaptation to changing environmental conditions. — **Abb. 1** The immediate environment of the root is called rhizosphere. It can be modulated by the plant in adaptation to changing environmental conditions.

The Pact project Chemical communication in the rhizosphere was funded with 1,2 million euros by the Leibniz association starting in April 2011. With this money the scientists of the Leibniz Institute of Plant Biochemistry (IPB) together with their cooperation partners at the Martin Luther University (MLU) and other non-university research institutes want to use ideas, technologies and competencies to get a better understanding of rhizosphere dynamics. In terms of the current state of knowledge, the root is hardly investigated. But it is known that roots can secrete substances into the soil, which can modulate their immediate environment. These substances consist of a mixture of sugars, proteins, organic acids, secondary substances and other components. The composition of these so-called root exudates is not constant. The nature and quantity of the components instead change dynamically due to the developmental stage of the plant (e.g. germination, growth, flowering and seed production) or in response to changing environmental factors.

Abb. 2 Model plant for mycorrhization: The root of Medicago truncatula in symbiosis with the mycorrhizal fungus Glomus intraradices. — **Abb. 2** Model plant for mycorrhization: The root of *Medicago truncatula* in symbiosis with the mycorrhizal fungus *Glomus intraradices*.

Subprojects

Within the Pact project a complete review of all components of the root exudates and their changes under specific conditions will be performed and documented. Toward this end, Arabidopsis thaliana will be grown under nutrient deficiency and the correlating root exudate patterns will be investigated. Another subproject involves the genetic background. Different plant species develop different patterns of exudates. These differences are genetically determined. Therefore 19 Arabidopsis ecotypes will be analyzed to clear up the association between the genetic constitution and exudate patterns. Furthermore the positive or negative effects of specific compositions of root exudates on microbe populations in the rhizosphere will be investigated. A final project comprises the inventory of all exudate components after contact of the roots with mycorrhizal fungi. Therefore the close interaction of the model plant Medicago truncatula with the fungus Glomus intraradices will be intensively studied.

Aims and objectives

With the knowledge of the exact chemical composition of the root exudates the association between root communication and plant vitality will be explained. The better understanding of the genetic regulation of the exudate production will lead in the future to the possibility of breeding more vital plant species, whose roots are able to „rule“ the chemical communication better than others and react therefore faster and more flexibly to adverse environmental conditions. Faced with urgent agronomic problems the partners of the Pact plan have responded with the initiation of an ambitious interdisciplinary rhizosphere consortium. „The biology of the rhizosphere is a major project“, says Dierk Scheel. „This is only manageable in cooperation with our partners.“

The Pact for Research and Innovation

is a federal funding initiative of the non-university research institutes, the counterpart to the Excellence Initiative, which funds German universities. Inside the Leibniz association the money of the Pact is distributed in terms of a competition among institution members. Every Leibniz Institute has the possibility to make an application only once a year. The IPB was already involved five times since the beginning of the funding period 2006, four of them as the main applicant. Other partners of the Pact project Chemical communication in the rhizosphere are the Leibniz Institute of Plant Genetics and Crop Plant Research in Gatersleben (IPK), the Leibniz Institute of Vegetable and Ornamental Crops Großbeeren (IGZ), the Helmholtz Centre for Environmental Research Halle (UFZ) and the Martin Luther University Halle-Wittenberg (MLU).