Carbon, Allocation, Transport and Signaling

IJPB Master 2 proposal

Role of tonoplastic sugar transporters in plant response to increased atmospheric CO2

Supervisor: Rozenn Le Hir, contact

Since the industrial revolution, there has been a continuous increase in atmospheric CO2 concentration, due to human activities (NOAA 2020). If CO2 accumulation continues at the same rate, its concentration is expected to reach around 1000 ppm by 2100 (Lobo et al. 2022). Plants are using atmospheric CO2, in association with light and water, to produce organic molecules with a carbon skeleton (e.g., soluble sugars, lipids, starch, parietal polysaccharides) through the process of photosynthesis. Plants are therefore important CO2 sinks and their vegetative growth is usually boosted when exposed to increased CO2 concentration. However, at the cell level, elevated CO2 (eCO2) conditions lead to adverse effects on several processes such as respiration and, ultimately, the energy production as well as all the energy-dependent processes (e.g., nitrogen assimilation, phloem loading, energized transport of photoassimilates) (Bhargava and Mitra 2021). In addition, the photosynthesis end-products have been shown to affect photosynthetic activity and gene expression (Paul and Pellny 2003). The control of the cytosolic sugar levels should therefore be highly regulated to ensure optimal photosynthesis. Sugars are compartmentalized into three main subcellular compartments among which the vacuole is the major sugar-storing organelle. The transport of sugars across the tonoplast thus represents an important control point to regulate the cytosolic sugar content. Several tonoplastic sugar transporters have been described (Hedrich et al. 2015), among which, the three tonoplastic members of the SWEET transporter family, namely SWEET2, SWEET16 and SWEET17 (Chardon et al. 2013; Klemens et al. 2013; Chen et al. 2015) are of particular interest since they are transporting sugars along the concentration gradient independently of energy. The objective of this project is therefore to explore the effects of a lack of the three tonoplastic SWEET transporters on plant photosynthetic performances under ambient and elevated CO2. We propose to use a multiscale approach including metabolites quantification, targeted gene expression analysis, chlorophyll fluorescence imaging (PAM imaging) and gas exchanges measurements). Therefore, during this M2 internship the student will have the opportunity to get an integrative view of the implication of these transporters in the plant response to climate change. Moreover, since SWEET transporters are known to dimerize to gain functionality, the student will also check the physical interaction between SWEET2, SWEET16 and SWEET17. The results acquired will help us to understand further how plants are handling sugars at the cellular level, and should allow us to propose new strategies to mitigate, in fine, the plant response to elevated CO2 which constitutes a crucial issue to explore in regards to plant yield.