Form for function: regulation of bundle sheath cell architecture for C4 photosynthesis

PROPOSAL SUMMARY The architecture of specialised cell types intricately aligns with cell function. A prime example is the bundle sheath (BS) cells of plants conducting C4 photosynthesis, in which CO2 is concentrated. This concentration mechanism increases photosynthetic efficiency by up to 50% compared to plants that use the more common C3 photosynthetic pathway. BS cells of C4 plants have two key adaptations: increased connectivity with adjacent mesophyll cells via numerous plasmodesmata that facilitate metabolite exchange for building CO2 concentration, and an increased number of organelles which are uniquely positioned at one side of the cell. Despite the proposed functional importance of these traits, it is not understood how they arise during leaf development.In this project, I aim to elucidate mechanisms governing BS cell architecture. I recently discovered that the polar localisation of plasmodesmata and organelles in BS cells occurs early in leaf development following light exposure in multiple C4 plants. I will use 3D electron microscopy to study BS cell development at high resolution in the C4 grass sorghum and mass spectrometry imaging to map key C4 metabolites, linking structure to metabolic function. I will then investigate molecular mechanisms involved in the development of both traits using mutants that are disrupted in components known to influence plasmodesmata development and organelle positioning in C3 species. I will identify additional components by looking for interaction partners of these components in C4 BS cells. In mutants showing defects in either trait, I will study the impact on metabolite gradients and photosynthetic efficiency, and will explore interdependency between the two polar traits. Overall, my project will reveal mechanisms essential for the development of leaf architecture in C4 plants, and will inform the design strategy for engineering C4 photosynthesis into C3 crops to increase yield.