Molecular Ecology of the Rhizosphere

research group Prof. Dr. Joost T. van Dongen

Low-oxygen stress

Molecular Response to the Oxygen Availibility

Romy Schmidt; Daan Weits (RWTH/SSSUP)

At present, hardly anything is known about the mechanisms by which plants recognise changes in the oxygen availability. It is suggested that the level of molecular oxygen within plant tissues could be sensed directly, but also indirect determination of the oxygen status, e.g. via the energy status or the level of NO is considered. We are investigating components of the molecular signal transduction pathway that act in plants to transmit information about the cellular oxygen status to the nucleus in order to control hypoxia induced gene expression. With this research we are especially focusing on the role of the transcription factor family of the Ethylene Response Factors (ERFs). Furthermore, custom-made micro-arrays, specially designed for the analysis of mitochondrial gene expression, are used to investigate gene expression on transcriptional level. To investigate changes in translational activity, a method to analyse the abundance of polysome-bound mRNA is established.

Metabolic Responses to the Oxygen Availability

Joost van Dongen, Junior Borella

Oxygen distribution through plant tissues is hampered by the high resistance for diffusion. Therefore, steep radial oxygen concentration gradients can occur in tissues that are not photosynthetically active. Moreover, roots generally face periods with oxygen depletion more often than shoots, due to flooding or waterlogging of the soil after a period of heavy rain. These strong differences in oxygen availability between various parts of a plant lead to compartmentalization of hypoxic and normoxic metabolism within a plant.

Extensive metabolome profiling in various plant species revealed a short-list with metabolites that accumulate under hypoxic conditions. Currently we are investigating how these metabolites are transported to plant organs that are well aerated and converted into substrates that are made available for hypoxic metabolism again. Such a “metabolic snorkel” would greatly enhance the metabolic efficiency during hypoxia and thus improve tolerance to low oxygen. Furthermore, both native and denaturing gel electrophoresis are used to analyze the effect of hypoxia and its related metabolic changes on the composition and activity of protein complexes and super-complexes of the mitochondrial electron transport chain.

It is well established that Nitric Oxide (NO) accumulates in plants during hypoxia. However, it is not clear yet what function NO has. It is suggested that NO could regulate the rate of respiration due to competitive inhibition of cytochrome c oxidase. A second putative function of NO production could be that the enzyme Nitrate reductase (i.e. the enzyme catalyzing the dominant production pathway of NO in plants) oxidises NADH, which could help to balance the redox status of the cytosol during hypoxia. Using a combination of transgenic and physiological experiments, we are characterising the NO production in plants and investigate the role of NO during hypoxia.