The Characterization of Cellulose Biosynthesis Regulators and Their Influence on Cell Wall Architecture

Open Access
- Author:
- Xin, Xiaoran
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 09, 2020
- Committee Members:
- Ying Gu, Dissertation Advisor/Co-Advisor
Ying Gu, Committee Chair/Co-Chair
Teh-Hui Kao, Committee Member
Joseph C. Reese, Committee Member
Sarah Mary Assmann, Outside Member
Paul Babitzke, Committee Member
Wendy Hanna-Rose, Program Head/Chair - Keywords:
- cellulose synthesis
cell wall
cellulose synthase - Abstract:
- Cellulose, the most abundant biopolymer on earth, is not only a critical component in the plant cell wall, but also an economically important source of food, paper, textiles, and biofuel. In higher plants, cellulose is synthesized by cellulose synthase (CESA) complexes (CSCs) at the plasma membrane. Various CESA auxiliary proteins have been shown to assist in the process of cellulose biosynthesis. In this dissertation, I aim to identify novel cellulose biosynthesis regulators and assess their influence on cell wall architecture. CELLULOSE SYNTHASE INTERACTIVE1 (CSI1) is a linker protein between CESAs and cortical microtubules (MTs), which guides the CSCs moving along MT trajectories. Loss of CSI1 results in defective CESA-MT coalignment, impaired anisotropic cell expansion, and reduced crystalline cellulose content. To further investigate how CSI1 affects cell wall structure, various spectroscopic techniques were utilized to examine the cell wall architecture in csi1-3 mutant. Transmission electron microscopy images of Arabidopsis outer epidermal cell wall revealed that csi1-3 lost the crossed-polylamellate wall architecture that was frequently observed in wild type seedlings. Despite the lack of CSI1, the most recently deposited cellulose microfibrils on the inner wall surface maintain a default transverse orientation, indicating that the orientation of nascent cellulose microfibrils is independent of CESA-MT linkage. A correlation between acid growth mediated cell elongation and the crossed-polylamellate cell wall architecture has been observed. This study may provide insights into the re-evaluation of the current models regarding cell morphogenesis. In addition to CSI1, a CALCIUM-DEPENDENT PROTEIN KINASE32 (CPK32) was identified as a putative CESA interactive partner in a yeast two-hybrid screen. The direct interaction between CPK32 and CESAs was validated in an in vitro pull-down assay. The dominant negative CPK32 transgenic plants exhibited deficiency in cellulose content as well as CSC motility, suggesting that CPK32 regulates cellulose biosynthesis. Considering the direct interaction between CPK32 and CESAs, the evidence that CPK32 phosphorylates CESA peptide, and the implication of CPK32 in cellulose synthesis, CPK32 might serve as a promising candidate for investigating the phosphorylation of CSCs. In this dissertation, the influence of a cellulose synthesis regulator, CSI1, on modifying cell wall architecture was assessed. A correlation between acid growth mediated cell elongation and crossed-polylamellate cell wall architecture was observed. Last, a novel CESA interactive protein, CPK32, was identified and characterized, which also provides the opportunity for future research on exploring its impact on CSC phosphorylation.