Pathogenesis-related (PR-1) proteins in cereals challenged with fungal pathogens

Alam, Shabnam (2001). Pathogenesis-related (PR-1) proteins in cereals challenged with fungal pathogens PhD Thesis, School of Molecular and Microbial Sciences, The University of Queensland.

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Author Alam, Shabnam
Thesis Title Pathogenesis-related (PR-1) proteins in cereals challenged with fungal pathogens
School, Centre or Institute School of Molecular and Microbial Sciences
Institution The University of Queensland
Publication date 2001
Thesis type PhD Thesis
Supervisor K.J. Scott
P.E. Ebert
Total pages 165
Collection year 2001
Language eng
Subjects L
270199 Biochemistry and Cell Biology not elsewhere classified
780105 Biological sciences
Formatted abstract

Systemic acquired resistance (SAR) is a broad physiological immunity in uninfected parts of the plant that results from local infection by a variety of pathogens. In the SAR response, a group of genes is expressed that encodes pathogenesis related (PR) proteins of which the PR-1 protein is the most abundant and is induced up to 1-2% of the total leaf protein. The biochemical function of the barley PR-1 protein is still unclear. The main objective of these studies was to characterize the nature of barley PR-1 protein and evaluate its importance in SAR and plant defence. The following aspects of the PRb-1 protein were investigated: 

1) A specific antibody for barley PRb-1 was raised in rabbit and this antibody was used to identify the presence and induction of the PRb-1 protein and to screen the transgenic wheat & barley transformed with the prb-1 gene. 

2) The local and systemic expression of the prb-1 gene and PRb-1 protein were examined in barley cultivar Psaknon plants following treatment of the primary leaves with either 2,6- dichloro-isonicotinic acid (INA) or Erysiphe graminis f.sp. hordei (Egh). A correlation between expression of PRb-1 protein and PRb-1 mRNA was established. Both the INA treated plants and Egh inoculated plants exhibited a similar strong systemic induction of the mRNA that was followed by a similar pattern of PRb-1 protein accumulation. Although the proteins accumulated more slowly and less transiently than the mRNA, they showed similar expression patterns. The induction of the PRb-1 protein after INA treatment was tissue specific with high levels of PRb-1 protein induced locally in primary leaves and systemically in secondary leaves while a low level of PRb-1 protein was induced in crown tissue after INA treatment but no induction of PRb-1 protein was detected in the roots. INA treated barley Psaknon plants induced strong SAR to subsequent Egh infection, the onset of which was correlated with induced expression of the PRb-1 protein in primary and secondary leaves. These results provided indirect evidence for antifungal activity of the PRb-1 protein against Egh. 

3) To study the effect of PRb-1 protein on fungal growth the coding region of barley prb-1 gene corresponding to putative mature PRb-1 protein was cloned and expressed in Escherichia coli. The in vitro expressed barley PRb-1 protein significantly reduced the germination of Egh spores. A direct fungicidal activity of PRb-1 protein against Egh was demonstrated by in-vivo tests in which the reduction of infected leaf surface was scored. This assay also showed that the inhibition on fungal growth by PRb-1 protein was dose dependent. 

4) Attempts were made to enhance the resistance against fungal pathogens in transgenic wheat and barley by introducing barley prb-1 gene and thereby strengthening the natural defence system of these crops. Transformation was performed by the bombardment of immature embryos with a plasmid containing both prb-1 and the marker bar gene under the constitutive ubiquitin promoter. Four PPT resistant ST0 wheat plants were selected from 6 separate experiments. In the T0 generation two plants were demonstrated to contain both prb-1 and bar genes. In addition, one plant was positive for the bar gene only and while another plant was negative for both the genes. Transmission of the bar and prb-1 gene to the T1 and T2 generation occurred but the segregation patterns of the genes varied among the progeny plants. Transgenic wheat plants expressed the prb-1 transgene in the T1 generation but the T2 generation of these plants failed to express the prb-1 transgene. 

Keyword Grain -- Diseases and pests
Grain -- Disease and pest resistance

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 17:40:32 EST