Identification of Genes That Regulate Systemic Acquired Resistance (SAR) in Arabidopsis thalianaEPA Grant Number: U915894
Title: Identification of Genes That Regulate Systemic Acquired Resistance (SAR) in Arabidopsis thaliana
Investigators: Anderson, Lisa K.
Institution: Duke University
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $96,764
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Molecular Biology/Genetics , Academic Fellowships , Biology/Life Sciences
The objective of this research project is to identify the genes that regulate systematic acquired resistance (SAR) in Arabidopsis thaliana. Plants are constantly under attack from a wide range of viral, fungal, and bacterial pathogens. One defense mechanism that allows the plant to resist infectious disease is known as the hypersensitive response (HR). During the HR, the infected plant cell recognizes that it is under attack, releases reactive oxygen species and antimicrobial compounds to kill the pathogen, initiates a programmed cell death response to kill the infected plant tissue, and sends out a systemic signal to the rest of the plant. This unknown systemic signal is dependent on salicylic acid (SA) and confers upon the plant a heightened resistance to subsequent infection with a broad range of virulent pathogens, or SAR.
In our laboratory, we have been studying the HR and SAR in A. thaliana through the study of the recessive constitutive expresser of pathogenesis-related genes (cpr5) mutant, which, under sterile conditions, spontaneously develops lesions that mimic the HR. As expected, this mutant also accumulates SA and is constitutively resistant to the virulent pathogens Pseudomonas syringae pv. maculicola ES4326 and Peronospora parasitica NOCO2. The cpr5 gene was cloned using a map-based approach and was found to encode a novel integral membrane protein unique to plants. To better understand the function of this protein in planta, three transgenic Arabidopsis lines were created and analyzed. A recombinant cpr5-green fluorescent protein that can be visualized using fluorescence microscopy was localized to the plasma membrane. A fusion of the cpr5 promoter to the GUS reporter gene was most highly expressed in tissues about to undergo developmentally regulated programmed cell death. The cpr5 protein driven by the constitutive CaMV 35S promoter resulted in a slight inhibition of cell death in response to external stimuli. From these transgenic lines, it can be inferred that the function of the cpr5 protein is to inhibit both pathogen-induced and developmentally regulated programmed cell death.
We also are using the cpr5 mutant to identify signaling components between the HR and SAR. A mutagenized population of cpr5 plants has been screened for mutants that continue to develop lesions that mimic the HR, but have lost constitutive resistance to P. parasitica NOCO2. This phenotype suggests that there is a second site mutation, which results in a defect in the initiation of SAR after the HR. Previous studies also have shown that the cpr5 mutant has constitutive resistance to P. parasitica NOCO2 in the absence of a functional NPRl protein, a well-studied positive regulator of SAR. This suggests that the cpr5 mutant activates an NPRl-independent resistance pathway. Therefore, I have performed the same mutant screen in the cpr5nprl double-mutant background. I currently am characterizing a mutant from each screen with the goal of isolating NPR1-dependent and NPRl-independent signaling components that regulate SAR.