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The physical landscape of plant cell energetics

Principal Supervisor: Dr Iain Johnston - School of Biosciences

Co-supervisor: George Bassel

PhD project title: The physical landscape of plant cell energetics

University of Registration: University of Birmingham

Project outline:

Plant bioenergetic organelles are pivotal players in feeding the world. The metabolic crosstalk between mitochondria and chloroplasts is responsible for a wealth of processes that regulate and control photosynthesis and plant-environment interactions. However, while modern science is making progress characterising the edges in these metabolic networks, the role of the rich and dynamic physical layout of the cell has largely been ignored.

In recent years, thanks to modern microscopy and fluorescently-labelled plant lines, the physical behaviour of plant organelles has been revealed in exquisite and rich detail. Far from the textbook picture of static, independent organelles, mitochondria and chloroplasts move through the cell like cars through a city (see data from the lab here). We have found that mutations that perturb this behaviour has physiological consequences [1], but a theoretical understanding of how these fascinating physical processes influence metabolism is currently absent.

An example of the importance of organelle position can be found in C4 photosynthesis. C4 is a remarkable, complex union of evolutionary innovations that has emerged from convergent evolution over 60 times. C4 offers many advantages over “traditional” C3 photosynthesis, but several important crop plants including rice and barley have not evolved C4. There is therefore great agricultural and economic interest in understanding how C4 emerges. Our previous work has shown that one step that may “prime” plants to proceed down this pathway is the rearrangement of organelles in cells [2]: in many C4 species, mitochondria and chloroplasts take up specific positions in some photosynthesising cell types [3]; tightly packed at one side of the cell relative to the vasculature. What does this arrangement bring to the cell? Can we mimic it in other crops to increase efficiency? More generally, how does the rich and controlled physical behaviour of plant organelles influence metabolism, and can we use this knowledge to rationally design better crops?

This project will use computational modelling to describe the physical environment of the cell and to analyse the links between physical and metabolic processes underlying plant bioenergetics. The student will use and refine computational models to describe the spatial and metabolic behaviour of model plant cells. In concert, confocal microscopy will be used to characterise organelle positioning in real plant cells, to inform the computational modelling approaches (see data from the lab above and here). The student will investigate the use of different chemical and genetically-encoded probes to characterise the levels of important metabolites in the cell, building a consistent picture of the physical “energy landscape” in individual plant cells.

This project would suit students interested in exploring vital but understudied aspects of cell biology – physical motion, intracellular heterogeneity in metabolites, and physical relationships between organelles. Some mathematical or computational background, and some experience of microscopy would be valuable, and enthusiasm in developing these interests is essential.

References:

  1. El Zawily et al., Plant Physiol 166 808 (2014)
  2. Williams & Johnston et al., eLife 2 e00961 (2013)
  3. Muhaidat et al., Plant Cell Environ 34 1723 (2011)

BBSRC Strategic Research Priority: Food Security

Techniques that will be undertaken during the project:

  • Physical modelling
  • Systems biology
  • Computer simulation
  • Plant growth
  • Genetic transformation
  • Live-cell imaging
  • Fluorescence microscopy

Contact: Dr Iain Johnston, University of Birmingham