Hanson, Johannes - Stress adaptation in plants

Research

Johannes Hanson standing in an in vitro plant growth room with a flask of plant cell culture in the handPhoto: Mattias Petterson Plants need highly efficient responses to adverse environmental conditions as they are bound to a single location. By totally changing their physiology plant can adapt to new environmental situations. These processes are in natural environments discriminative for plant fitness and in agricultural systems determining yield. Reprogrammed metabolism and changed translational patterns are important elements of stress adaption. The goal of the group is to understand how plants adjust their metabolism and translation in response to a changing environment. On the longer term we want to use this knowledge to design better trees and crops.

Adverse environmental conditions often cause limited energy availability and plant cells respond to this by reprograming their metabolism to better fit the new situation. This dramatic change involves hundreds of gene products and metabolites; we call this the Low Energy Syndrome, LES. The change is mastered by the SnRK1 kinase complex, which is able to react to low levels of metabolizable sugars. This parallels the manner in which all eukaryotes regulate starvation responses. In plants the SnRK1 kinases regulate gene expression of genes encoding key metabolic enzymes by activating certain bZIP transcription factors. One of our projects focuses on these transcription factors. We are interested in their mode of action and how their activity is regulated. Technically we are using high throughput expression analysis (massive sequencing) and metabolic profiling as central analysis tools combined with genetics and transgene based methods.

Illustration of the signalling pathway activated by stress Low energy availability and stress activate signaling cascades in the plant, initiated by activation of the SnRK1 kinase and resulting in changed metabolism and growth – The Low Energy Syndrome (LES). The aspects of interests for us are indicated.

When conditions are favorable for plant growth the SnRK1 complex is deactivated and a second major signaling system takes over mastered by another kinase - The Target of rapamycin, TOR that is positively regulates growth in all eukaryotes. TOR does so partly by regulating translation, which is a very energy consuming process and is therefore tightly regulated. The second major project in the laboratory deals with the regulatory mechanism of translational control by focusing on the activity of the ribosome. We currently are identifying novel components involved in translational changes using transcriptomics, translatomics, proteomics and genetic methodology.

The growing population of this planet will change our society. It is clear that food, feed and other plant-based resources will be limiting in the future. The grand challenge is to increase plant production a sustainable way. The transition to less fossil fuel dependent production will challenge our agricultural systems even further. Consequently, there is a basic need to optimize plant growth. This can be done by changed growth practices and reducing post-harvest losses, etc. However, we must use crop improvement to reach increased productivity similarly the green revolution half a decade ago. This is not limited to classical crops. We will need novel corps for biomass, bioenergy and biorefinery needs. By understanding the underlying mechanisms of growth-control we hope to find new ways to improve plant based production.

The figure illustrates how translation activity is assayedTranslation is assayed using density gradients where polysomes (P, translating ribosomes) are separated from monosomes (M, non-translating ribosomes). Translation varies dramatically depending on experimental condition or developmental changes A) Translation is inhibited by 6h extended night and increased by sucrose treatments (6 h treatment of 100 mM sucrose), as indicated by increased relative levels of polysomes. Sucrose treatments compensate for the extended night treatment and allow continued translation although low energy input from the light. B) Ribosomal preparation from germinating seeds showing primarily monosomes in dry seeds (0h) and more translation (polysomes) during germination (5 to 72 hours) (Bai et al., 2017). C) In poplar buds, with primary monosomes present in the dormant winter buds and increased translation as the bud growth is initiated during the spring as evident from increased polysome levels (André and Mahboubi, unpublished). D) By Using RiboSeq we can map the translational activity of single ribosomes to mRNAs Image indicate the ribosomes bound to mRNA and after degrading the parts of the mRNA that is not bound by ribosome we can sequence the protected fragments. E) Resulting patterns of mapped reads (blue bars) representing fragments translated by active ribosomes on a mRNA sequence (red bars, thick parts representing Open reading frames). Distance between the ticks on the scale is 5 kbp.