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Pathogenicity test of different strains of Erwinia amylovora bacterium including hrpN − , dspA/E − and hrpW − mutants compared with wild type strain and mock control on immature pear fruit (Pyrus communis cv. Louise Bonne of Jersey). The image is representative of 10 replications
Source publication
Fire blight caused by the gram-negative bacterium Erwinia amylovora is the most destructive disease of pome fruit trees. The pathogen induces the disease by secreting HrpN, HrpW, and DspA/E effector proteins into host tissues triggering oxidative burst. To study the role of these effectors in the course of interaction with host plants, hrpN−, hrpW−...
Citations
The resistant phenotype of pear cultivars includes either complete resistance or tolerance to the attack by the causative agent of fire blight. The effect of ferritin and active iron (Fe2+) concentrations was compared in resistant (Dargazi), tolerant (Harrow Sweet), and susceptible (Bartlett) pear cultivars inoculated with a wild type strain of Erwinia amylovora (Ea273). The examination of necrosis revealed that resistance to the disease manifested itself as a delay in the appearance of symptoms and progression of the disease. Despite a rise in ferritin levels in all cultivars following disease agent inoculation, resistant and tolerant cultivars showed greater ferritin levels than susceptible cultivar. In addition, only resistant and tolerant cultivars displayed a drop in Fe2+ levels. The rate of decrease in Fe2+ content in Dargazi and Harrow sweet cultivars was 28 and 33%, respectively. Hydrogen peroxide (H2O2) and hydroxyl radical (OH•−) accumulation and intensities were considerably distinctive. Furthermore, tolerant and sensitive cultivars started producing OH•− radicals faster than resistant cultivar. According to these findings, different pathways are employed by pear cultivars to respond to the causative agent of fire blight.
HarpinEa protein can stimulate plants to produce defense responses to resist the attack of pathogens, improve plant immune resistance, and promote plant growth. This has extremely high application value in agriculture. To efficiently express soluble HarpinEa protein, in this study, we expressed HarpinEa protein with a 6× His-tag in Escherichia coli BL21 (DE3). Because of the low level of expression of HarpinEa protein in E. coli, three rounds of synonymous codon optimization were performed on the +53 bp of the translation initiation region (TIR) of HarpinEa. Soluble HarpinEa protein after optimization accounted for 50.3% of the total soluble cellular protein expressed. After purification using a Ni Bestarose Fast Flow column, the purity of HarpinEa protein exceeded 95%, and the yield reached 227.5 mg/L of culture medium. The purified HarpinEa protein was sensitive to proteases and exhibited thermal stability. It triggered visible hypersensitive responses after being injected into tobacco leaves for 48 h. Plants treated with HarpinEa showed obvious growth-promoting and resistance-improving performance. Thus, the use of TIR synonymous codon optimization successfully achieved the economical, efficient, and soluble production of HarpinEa protein.
