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Type: Theses
Title: The role of barley cell wall polysaccharides in host plant defence mechanisms against powdery mildew
Author: Chowdhury, Md Jamil
Issue Date: 2016
School/Discipline: School of Agriculture, Food and Wine
Abstract: • The cell wall is the first line of plant defence, presenting a barrier that protects cells from infectious pathogens in the surrounding environment. Plants respond dynamically to pathogen attack at the cell wall level by developing papillae at the infection site. In many plant/pathogen interactions, papillae formation is an important determinant of pre-invasion resistance by the host species. While many aspects of papillae are known, the cell wall components responsible for making papillae an effective barrier to fungal penetration are not fully understood. This project aimed to define the role of cell wall polysaccharides in the papillae-based penetration resistance mechanism of barley. Using the barley-powdery mildew host-pathogen system, papillae polysaccharide composition and the genetic factors responsible for their biosynthesis were examined. • Here it is demonstrated that the major polysaccharides found in barley papillae are callose, arabinoxylan and cellulose. The papillae are layered with an inner core consisting of callose and arabinoxylan and an outer layer containing arabinoxylan and cellulose. A higher level of polysaccharide staining at non-penetrated papillae compared to the penetrated papillae was observed and this suggested that the polysaccharides are necessary components of the papillae-based penetration resistance mechanism of host plants. • The members of the Glucan synthase-like (Gsl)gene family found in the barley genome have been characterised and identified and when HvGsl6 was silenced this resulted in a loss of callose in the papillae and an increased rate of successful fungal penetration. • A number of candidate genes from several glycosyltransferase families suspected to be associated with the biosynthesis of arabinoxylan in papillae have been identified. Transient down-regulation and up-regulation of the individual candidate genes using a biolistic DNA delivery system led to an altered level of susceptibility to powdery mildew. However, the highest levels of resistance were observed when GT43 (MLOC_54026) and the GT47 (MLOC_14407) genes were over-expressed together. These genes are putatively involved in arabinoxylan backbone biosynthesis. • Furthermore, this PhD study also contributed to the characterisation of the role of the HvCslD2 gene in non-host resistance, a project led by Dr. Patrick Schweizer, IPK, Germany. We showed that silencing of the HvCslD2 gene in barley results in reduced cellulose accumulation in the papillae during powdery mildew infection, suggesting that HvCslD2 is a key gene involved in cellulose biosynthesis in papillae. • The association of high levels of arabinoxylan and cellulose deposition in papillae with the penetration resistance mechanism of the host plant, provides new targets for the improvement of papilla composition. The identification of the genes involved in the biosynthesis of each papilla component will provide new targets for the generation of novel crop lines with greater disease resistance.
Advisor: Burton, Rachel Anita
Fincher, Geoffrey Bruce
Little, Alan
Dissertation Note: Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2016.
Keywords: powdery mildew
Blumeria graminis
plant cell wall
plant-pathogen interactions
host disease resistance
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
DOI: 10.25909/5b3eba4e947f1
Appears in Collections:Research Theses

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