Résumé
Although plants only require small amounts of manganese (Mn), its availability in soils is often a limiting factor for their proper development. Mn is essential for important metabolic pathways such as photosynthesis but can be toxic when accumulated in excess. The maintenance of cellular Mn homeostasis is therefore crucial. In Arabidopsis root cells, Mn is taken up by the high-affinity transporter NRAMP1 (Cailliatte et al., 2010). Our recent studies characterized the regulation of the subcellular dynamics of this transporter in response to Mn availability. NRAMP1 is stabilized at the plasma membrane under Mn deficiency and internalized in response to Mn excess in a phosphorylation-dependent manner (Castaings et al., 2021). The actors of this signaling are however still unknown. This thesis work aims (i) to identify the kinase(s) responsible for the phosphorylation of NRAMP1 in response to Mn and (ii) to characterize their role in Mn homeostasis. Exposure to excessive Mn amounts triggers calcium signaling by kinases from the CIPKs (CBL-Interacting Protein Kinase) and CPKs (Calcium-dependent Protein Kinase) families to promotes Mn detoxification in the vacuole (Zhang et al., 2021; Ju et al., 2022). Given that these kinases are also involved in the regulation of numerous transporters at the plasma membrane (Tang et al., 2020), they are prime candidates to be responsible of NRAMP1 phosphorylation under Mn stress. We developed several approaches to test this hypothesis and our latest results will be presented in this poster. Cailliatte, R., Schikora, A., Briat, J. F., Mari, S., & Curie, C. (2010). High-affinity manganese uptake by the metal transporter NRAMP1 is essential for Arabidopsis growth in low manganese conditions. The Plant cell, 22(3), 904–917. Castaings, L., Alcon, C., Kosuth, T., Correia, D., & Curie, C. (2021). Manganese triggers phosphorylation-mediated endocytosis of the Arabidopsis metal transporter NRAMP1. The Plant journal : for cell and molecular biology, 106(5), 1328–1337. Ju, C., Zhang, Z., Deng, J., Miao, C., Wang, Z., Wallrad, L., Javed, L., Fu, D., Zhang, T., Kudla, J., Gong, Z., & Wang, C. (2022). Ca2+-dependent successive phosphorylation of vacuolar transporter MTP8 by CBL2/3-CIPK3/9/26 and CPK5 is critical for manganese homeostasis in Arabidopsis. Molecular plant, 15(3), 419–437. Tang, R. J., Wang, C., Li, K., & Luan, S. (2020). The CBL-CIPK Calcium Signaling Network: Unified Paradigm from 20 Years of Discoveries. Trends in plant science, 25(6), 604–617. Zhang, Z., Fu, D., Sun, Z., Ju, C., Miao, C., Wang, Z., Xie, D., Ma, L., Gong, Z., & Wang, C. (2021). Tonoplast-associated calcium signaling regulates manganese homeostasis in Arabidopsis. Molecular plant, 14(5), 805–819.