School of BioSciences - Theses
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ItemUnderstanding the role of companion of cellulose synthase1 (CC1) in maintaining cellulose synthesis under salt stress( 2022)Salt stress is one of the most detrimental abiotic stresses for plants, and substantially impacts plant biomass and agricultural productivity. In the last decades, revealing how plants cope with stress conditions and maintain growth under salt stress has been an important focus in plant research and agricultural development. The plant cell wall, which encases plant cells and functions as a cellular exoskeleton, is an important structure to cope with such stresses. One of the main components of the cell wall is cellulose, which is synthesized by cellulose synthase (CESA) complexes (CSC) at the plasma membrane by moving along underlying cortical microtubules. COMPANION OF CELLULOSE SYNTHASE (CC) 1 and 2 are components of the CSCs and links the CSCs to the microtubules. CC1 and CC2 function in maintaining cellulose synthesis under salt stress by supporting microtubules and CESA behaviors. However, the exact regulatory mechanisms of the CC1 and CC2 proteins remain largely unknown. In this thesis, the regulatory mechanisms of CC1 are investigated in more details. In Chapter 2, a comprehensive phylogenetic analysis shows that the CC protein family contains up to seven members in land plants, with six CCs present in the Arabidopsis thaliana (A. thaliana) genome. The chimeric constructs swapping the N-terminus of CC1 with different homologs, i.e., CC2-CC6, were generated and transformed into cc1cc2 double mutants. The phenotypic analyses showed that CC1 to CC4 and CC6 behaved similar to CC1 in supporting plant growth under salt stress, while CC5 did not. These inabilities of CC5 were due to its defects in microtubule-binding, microtubule bundling, and maintenance of microtubules stability under salt stress, as well as other changes in functionalities of the N-terminal part of the protein. CC5 was found to have a dominant negative effect on plant root growth. Furthermore, CC5 was specifically expressed in pollen and inhibited pollen germination under salt stress. These findings reveal functional differences among CC protein family members and improve our understanding of the four microtubule-binding motifs of CC1. In Chapter 3, an immunoprecipitation-mass spectrometry (IP-MS) analysis was performed to identify potential interactors of CC1 under normal conditions and salt stress. Among the candidates, FERONIA (FER) was selected for further study. It was found that FER interacted and phosphorylated CC1, and the phosphorylation of CC1 by FER negatively affected its in vitro microtubule-binding and microtubule-bundling abilities. In Chapter 4, in planta phospho-proteomic analysis was performed and potential phosphorylation sites of CC1 were identified. Here, BRASSINOSTEROID INSENSITIVE 2 (BIN2) was found to phosphorylate CC1, and the relevant phospho-null and phospho-mimetic mutants were generated and briefly characterized. These findings provide further insights into the regulatory mechanisms of CC1, which are important to better understand how plants maintain cellulose synthesis and growth under salt stress.