Progress 01/01/03 to 12/31/03
Outputs
The apple acreage in Michigan has declined by about 18% in the last five years; severe fire blight epidemics in 1998 and 2000 contributed significantly to this reduction in the size of the Michigan apple industry. New strategies are needed for controlling fire blight. The objectives of this proposal are to integrate new control strategies based on growth regulation, boosting the resistance of apple trees, and antibiotics into disease management programs; characterize the genetic variation between Erwinia amylovora and closely related species; evaluate the transgenic expression of the MpNPR-1 gene in apple, and characterization of the Hrp virulence system in E. amylovora. We determined that the apple growth regulator Apogee can be successfully substituted for one spray of streptomycin for field control. This is significant because of the problems with streptomycin resistant E. amylovora present in many Michigan orchards. We used genetic evidence from chromosomal and
plasmid DNA analyses to determine that Japanese Erwinia strains infecting pear were more related to E. pyrifoliae than E. amylovora. We continued our work on the role of the ubiquitous plasmid pEA29 in virulence. We have shown that expression of many of the promoters of pEA29 genes is induced during infection and are currently constructing knockout mutations in several of the genes for functional characterization. We initiated a study designed to identify E. amylovora genes specifically induced during infection. We screened 19,200 clones containing random fragments of E. amylovora chromosomal DNA and found that 863 (4.5%) were induced during infection. We are currently sequencing these DNA fragments and will use standard methods for gene identification. Selected sequences will then be further analyzed by mutation and functional characterization during infection. Research on the apple NPR1 gene and the E. amylovora hrpA and dspE genes is longer term but offers the promise of finding
novel control strategies. A version of the apple NPR1 gene that is constitutively expressed was successfully transformed into the fire blight susceptible apple cultivar Galaxy. These transformants show significant resistance to fire blight, and possibly also to other apple diseases. We are developing an antibody against the NPR1 protein so that the quantity of protein produced in transgenic lines can be accurately determined and correlated with plant resistance. The Hrp virulence system is a secretion system that plays a critical role in the pathogenicity of E. amylovora on apple. The HrpA protein is a major component of this system. Substantial progress was made using nuclear magnetic resonance to solve the tertiary structure of the HrpA protein. We are continuing work on determining the function of the DspE protein and have evidence that it functions as s suppressor of apple cell wall defense. Understanding the function of this critical pathogenicity protein may lead to effective
strategies designed to counteract its effects.
Impacts
Research on genes required for virulence of the fire blight bacterium may offer the promise of finding novel control strategies, including the rational design of control compounds for fire blight. These strategies will ultimately impact host resistance, a disease management strategy that is environmentally friendly and should prove durable.
Publications
- Maxson-Stein, K., G.C. Mcghee, J.J. Smith, A.L. Jones, and G.W. Sundin. 2003. Genetic analysis of a pathogenic Erwinia sp. isolated from pear in Japan. Phytopathology 93:1393-1399.
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Progress 07/01/02 to 06/30/03
Outputs
The apple acreage in Michigan has declined by about 18% in the last five years; severe fire blight epidemics in 1998 and 2000 contributed significantly to this reduction in the size of the Michigan apple industry. New strategies are needed for controlling fire blight. The objectives of this proposal are to integrate new control strategies based on growth regulation, boosting the resistance of apple trees, and antibiotics into disease management programs; characterize the genetic variation between Erwinia amylovora and closely related species; evaluate the transgenic expression of the MpNPR-1 gene in apple, and characterization of the Hrp virulence system in E. amylovora. We used genetic evidence from chromosomal and plasmid DNA analyses to better understand the relationship between E. pyrifoliae, a necrosis-inducing Erwinia bacterium from Asian pears, and E. amylovora. This work confirmed that E. pyrifoliae constituted a distinct Erwinia species. Field research
determined that streptomycin is still the most effective bactericide available for fire blight control; however, we also found E. amylovora strains resistant to streptomycin in two important apple-growing areas of Michigan. Additional work showed that the alternative antibiotic oxytetracycline performs well but not excellent in blossom blight control and copper, although effective, is limited in time of use due to problems with fruit russeting. The growth regulator prohexadione calcium was excellent in limiting secondary shoot blight infections and the biological control agent Serenade was partially effective in disease control. Research on the apple NPR1 gene and the E. amylovora hrpA and dspE genes is longer term but offers the promise of finding novel control strategies. A version of the apple NPR1 gene that is constitutively expressed was successfully transformed into the fire blight susceptible apple cultivar Galaxy. Preliminary results of transformants suggest that the
transgenic apple plants are boosted in their resistance to fire blight infection.
Impacts
Research on genes required for virulence of the fire blight bacterium may offer the promise of finding novel control strategies, including the rational design of control compounds for fire blight. These strategies will ultimately impact host resistance, a disease management strategy that is environmentally friendly and should prove durable.
Publications
- Schnabel, E.L., G.C. McGhee, and A.L. Jones. 2002. Comparison of groEL sequences, 16S-23S rDNA spacers, and pEa29-type plasmids from Erwinia amylovora and E. pyrifoliae. Acta Hort. 590:429-439.
- McGhee, G.C., E.L. Schnabel, K. Maxson-Stein, B. Jones, V.K. Stromberg, G.H. Lacy, and A.L. Jones. 2002. Relatedness of chromosomal and plasmid DNAs of Erwinia pyrifoliae and Erwinia amylovora. Appl. Environ. Microbiol. 68:6182-6192.
- McGhee, G.C., G.C. Foster, and A.L. Jones. 2002. Genetic diversity among Erwinia amylovora's ubiquitous plasmid pEa29. Acta Hort. 590:413-421.
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Progress 01/01/02 to 12/31/02
Outputs
The apple acreage in Michigan has declined by about 18% in the last five years; severe fire blight epidemics in 1998 and 2000 contributed significantly to this reduction in the size of the Michigan apple industry. New strategies are needed for controlling fire blight. The objectives of this proposal are to integrate new control strategies based on growth regulation, boosting the resistance of apple trees, and antibiotics into disease management programs; characterize the genetic variation between Erwinia amylovora and closely related species; evaluate the transgenic expression of the MpNPR-1 gene in apple, and characterization of the Hrp virulence system in E. amylovora. We used genetic evidence from chromosomal and plasmid DNA analyses to better understand the relationship between E. pyrifoliae, a necrosis-inducing Erwinia bacterium from Asian pears, and E. amylovora. This work confirmed that E. pyrifoliae constituted a distinct Erwinia species. We used genetic
variations in pEa29, a plasmid that is conserved among all E. amylovora strains, to trace the geographic distribution and movement of this species. We have also initiated similar work in analyzing Erwinia strains from Japan that are related to E. amylovora. Research on the apple NPR1 gene and the E. amylovora hrpA and dspE genes is longer term but offers the promise of finding novel control strategies. A version of the apple NPR1 gene that is constitutively expressed was successfully transformed into the fire blight susceptible apple cultivar Galaxy. Preliminary results of transformants suggest that the transgenic apple plants are boosted in their resistance to fire blight infection. We are developing an antibody against the NPR1 protein so that the quantity of protein produced in transgenic lines can be accurately determined and correlated with plant resistance. The Hrp virulence system is a secretion system that plays a critical role in the pathogenicity of E. amylovora on apple.
The HrpA protein is a major component of this system. Substantial progress was made using nuclear magnetic resonance to solve the tertiary structure of the HrpA protein. Also, we have constructed transgenic plants using the model host Arabidopsis that express the E. amylovora dspE gene in order to understand the function of the DspE protein and its effect on plants. Understanding the function of this critical pathogenicity protein may lead to effective strategies designed to counteract its effects.
Impacts
Research on two genes required for virulence of the fire blight bacterium may offer the promise of finding novel control strategies, including the rational design of control compounds for fire blight. These strategies will ultimately impact host resistance, a disease management strategy that is environmentally friendly and should prove durable.
Publications
- McGhee, G.C., E.L. Schnabel, K. Maxson-Stein, B. Jones, V.K. Stromberg, G.H. Lacy, and A.L. Jones. 2002. Relatedness of chromosomal and plasmid DNAs of Erwinia pyrifoliae and Erwinia amylovora. Appl. Environ. Microbiol. 68:6182-6192.
- McGhee, G.C., G.C. Foster, and A.L. Jones. 2002. Genetic diversity among Erwinia amylovora's ubiquitous plasmid pEa29. Acta Hort. 590:413-421.
- Schnabel, E.L., G.C. McGhee, and A.L. Jones. 2002. Comparison of groEL sequences, 16S-23S rDNA spacers, and pEa29-type plasmids from Erwinia amylovora and E. pyrifoliae. Acta Hort. 590:429-439.
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