Resolving the central metabolism of Arabidopsis guard cells

Photosynthesis and water use efficiency, key factors affecting plant growth, are directly controlled by microscopic and adjustable pores in the leaf-the stomata. The size of the pores is modulated by the guard cells, which rely on molecular mechanisms to sense and respond to environmental changes. It has been shown that the physiology of mesophyll and guard cells differs substantially. However, the implications of these differences to metabolism at a genome-scale level remain unclear. Here, we used constraint-based modeling to predict the differences in metabolic fluxes between the mesophyll and guard cells of Arabidopsis thaliana by exploring the space of fluxes that are most concordant to cell-type-specific transcript profiles. An independent C-13-labeling experiment using isolated mesophyll and guard cells was conducted and provided support for our predictions about the role of the Calvin-Benson cycle in sucrose synthesis in guard cells. The combination of in silico with in vivo analyses indicated that guard cells have higher anaplerotic CO2 fixation via phosphoenolpyruvate carboxylase, which was demonstrated to be an important source of malate. Beyond highlighting the metabolic differences between mesophyll and guard cells, our findings can be used in future integrated modeling of multicellular plant systems and their engineering towards improved growth

Protein-protein interactions and metabolite channelling in the plant tricarboxylic acid cycle

Protein complexes of sequential metabolic enzymes, often termed metabolons, may permit direct channeling of metabolites between the enzymes, providing increased control over metabolic pathway fluxes. Experimental evidence supporting their existence in vivo remains fragmentary. In the present study, binary interactions of the proteins constituting the plant tricarboxylic acid (TCA) cycle are tested. Affinity purification-mass spectrometry, split-luciferase and yeast-two-hybrid assays are employed and the (semi-)quantitative results from these methods are integrated to generate a single reliability score for assessing protein-protein interactions. By this approach, 158 interactions including those between the catalytic subunits of sequential enzymes and many novel interactions between subunits of enzymes mediating non25 adjacent reactions are identified. Channeling of citrate and fumarate in isolated potato mitochondria are revealed by isotope dilution experiments. These results provide the evidence for a functional TCA cycle metabolon in plants which we discuss in the context of contemporary understanding of this pathway in other kingdoms

On the Elaborate Network of Thioredoxins in Higher Plants

International audienc