Periodic Reporting for period 1 - SugarOsmoSignalling (Analysis of sugar- and osmo-signalling mechanisms in cell wall integrity maintenance)
Periodo di rendicontazione: 2016-03-16 al 2018-03-15
In this project, we investigated the mode of action of the plant CWI maintenance in the flowering plant Arabidopsis thaliana, which is frequently used as green test tube to facilitate targeted follow up studies in crop species. We were interested in understanding how plants detect cell wall damage and how the initial signal is passed on to activate downstream responses. Previously it was shown that carbohydrate metabolism is strongly affected by cell wall damage. Here we aimed to elucidate how metabolic signalling could be involved in the CWI maintenance mechanism. Since cell wall damage occurs frequently during pathogen infections, another objective of our work was to elucidate the coordination of pathogen defence with CWI maintenance. Finally, we aimed to increase our knowledge on the influence of osmotic pressure on cell wall damage responses.
In summary, we identified novel components required for osmo-sensitive CWI maintenance signalling and successfully gained insights into the mechanism coordinating pathogen defence with CWI maintenance. This increased understanding of the regulatory mechanisms will facilitate generation of novel crop varieties, which allow food and bioenergy production in a more sustainable manner.
The phenotypic clustering showed that genes required for pattern-triggered immunity are inhibiting cell wall damage signalling. In addition, RNA-Sequencing of isoxaben-treated seedlings indicated that a danger-associated molecular pattern response is triggered through plant elicitor peptides (Peps). Indeed further experiments showed that Pep precursor genes are transcriptionally induced and the corresponding proteins secreted into the apoplast. To understand the function of Pep signalling during CWI impairment, seedlings exhibiting or lacking functional Pep receptors at the plasma membrane were co-treated with synthetic Peps and isoxaben. These experiments showed that Pep detection leads to reduced isoxaben-dependent phytohormone accumulation. As Pep signalling is also induced during pathogen-associated molecular pattern-triggered immunity, where it acts as defence signalling amplifier, our data reveal a mechanism potentially fine-tuning immune signalling and CWI signalling.
In order to investigate the role of metabolic signalling for CWI signalling, we analysed isoxaben responses in seedlings affected in trehalose-6-phospate metabolism (T6P), glycerol-3-phosphate metabolism (G3P) and nitrogen metabolism, respectively. Altered T6P or G3P metabolism affected isoxaben responses, but no clear correlation with metabolite abundance could be found. Instead, loss of nitrate reductase function strongly repressed isoxaben effects on hormone accumulation, lignification and cell cycle gene expression. The data suggest that alterations in T6P and G3P content influence the extent of isoxaben responses, while nitric oxide signalling through nitrate reductase activity might be essential for CWI maintenance.
Hyperosmotic conditions reduce the magnitude of cell wall damage responses. We show that cellulose biosynthesis inhibition and enzymatic degradation cause different structural cell wall damage, but similar osmo-sensitive responses. Several plasma membrane-localized proteins are known to be required for detection of osmotic stress. However, none of the osmosensors tested in our experiments was required for osmotic suppression. Current evidence suggests that mechanical signalling is of major importance for this osmo-sensitive mechanism.
Data obtained during the project period have been presented at several international conferences in Norway, Austria, the United Kingdom, Finland and Germany.