Identification and characterization of DUF288 (Domain of Unknown Function 288) proteins required for cell wall synthesis

Restricted (Penn State Only)
Author:
Liu, Jingrui
Graduate Program:
Biochemistry, Microbiology, and Molecular Biology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 30, 2017
Committee Members:
  • Ying Gu, Thesis Advisor
  • Xin Zhang, Committee Member
  • Lu Bai, Committee Member
Keywords:
  • glycosyltransferase
  • polysaccharides
  • cell wall synthesis
  • Arabidopsis
  • plants
Abstract:
The plant cell wall is mainly composed of polysaccharides that can be further divided into cellulose and non-cellulosic polysaccharides. Cellulose is synthesized by cellulose synthase complexes (CSCs) at plasma membrane while non-cellulosic polysaccharides are synthesized by glycosyltransferases in the Golgi apparatus and then exported to the cell wall. Currently, the majority of the cell wall synthesis related proteins are still unknown. Identification and characterization of novel proteins are crucial to decipher the molecular mechanisms underlying cell wall synthesis. In this thesis, I identify DUF288 (Domain of Unknown Function 288) proteins as novel cell wall synthesis related proteins by co-expression analysis and reverse genetics. Mutations in DUF288 proteins cause cellulose deficiency in both primary and secondary cell wall. However, DUF288 proteins do not affect CSC assembly, suggesting that DUF288 proteins might not directly mediate cellulose synthesis by regulating CSC activity. DUF288 proteins are predicted to function as glycosyltransferases based on their subcellular localization in Golgi-like cytoplasmic compartments. In support of this hypothesis, putative glycosyltransferase domain is important for the function of DUF288 proteins. In addition, mutations in DUF288 proteins exhibited altered cell wall composition and reduced mucilage staining, indicating that DUF288 proteins are required for non-cellulosic polysaccharide biosynthesis. In conclusion, this work will be able to not only characterize functions of DUF288 proteins required for cell wall synthesis but also enable us to draw a complete picture about the function of polysaccharides in plant growth and development.